How To Instantly Convert Weeks to Minutes

Published on Sunday, September 21, 2014 in , , ,

Tfa1964's photo of the Zimmer tower at Lier, BelgiumA little over a year ago, I teased Grey Matters readers with a mystery skill. First, they had to learn to easily multiply by 63, then learn how to easily multiply by 72. The skill itself was revealed to be how to roughly convert any whole number of years into seconds!

In this post, you'll learn a similar skill: how to convert weeks into minutes instantly!

Back in the days before computers and calculators, this was a popular feat among entertainers who performed as human calculators. It was quick and direct to perform, yet was highly impressive to audiences.

One week has 7 days, and each day has 24 hours. Every hour, of course, has 60 minutes, so if we multiply out 1 week × 7 days/week × 24 hours/day × 60 minutes/hour, we get 10,080 minutes in a week. The number 10,080, as it happens is very easy to multiply by almost any number of weeks. If you keep the number of weeks at or below 124 (about 2.37 years), the numbers are even easier to work out.

STEP 1: Ask for any number of weeks less than 2 years (104 weeks). As an initial example, we'll say an audience member gave the number 36.

STEP 2: Write down the number they just gave you. In our example, you'd write 36.

STEP 3: Multiply this number by 8 in your head, and write this result to the immediate right of the first number you wrote. This is simpler than it sounds; all you have to do is double the number 3 times. For 36, doubling once gives you 72, doubling a second time gives you 144, and doubling a third times gives you 288. Writing 288 next to the 36 you wrote earlier gives you 36288.

NOTE: In step 3, it's very important to always treat the answer as a 3-digit number. For weeks from 13 to 104, it will be, but for weeks from 2 to 12, it will be a 2-digit number. You can change this into a 3-digit number simply by adding a 0 to the left of it. If you're given 7 weeks in step 1, you write down the 7 as in step 2, then multiply 7 × 8 to get 56, which becomes 056. You would write 056 as your step 3 answer, giving 7056, and then continue with step 4.

STEP 4: Write a zero to the immediate right of the other numbers, add commas where appropriate, and you're done! In our example, we add the zero to the right, giving us 362880. With commas, that result is 362,880. This means that there are 362,880 minutes in 36 weeks!

With a little practice, you'll be astounded as to how quickly you can pick this impressive skill up. You can quiz yourself by having Wolfram|Alpha give you a random number of weeks from 2 to 104, and then use it to verify whether you've worked out the correct answer.

HANDY BONUS TIP: You can make this more impressive for an audience by having someone with a calculator verify this in a long, drawn-out manner. Tell them to put in the number of weeks given, then multiply by 7 for the number of days in a week, then multiply by 24 hours in a day, and then multiply by 60 minutes in a week. Multiplying it out the long way makes this feat seem more difficult, as you're hiding the simple 10,080 conversion factor.

Try it out and amaze your friends!


Days and Knights

Published on Sunday, September 14, 2014 in , , , ,

Mbdortmund's chess knight photo with DafneCholet's Calendar* photoAs you can probably tell from this recent post and this recent post, I've spent quite a bit of time thinking about the Knight's Tour lately.

These thoughts have reminded of a different type of Knight's Tour puzzle. This unusual variation involves moving the knight around a calendar.

It was 4 years ago, during September or October, that I was looking for blog post inspirations and ran across a thread on the XKCD forums, titled “Knight's Tour revamped”, which suggested playing the Knight's Tour on a calendar.

There was an added challenge, however: With your starting square being considered as move #1, how many dates could you land on that were the same as the move number? For example, if move #1 started on the 1st of the month, both the move number and the date would be 1.

As you can see in the original thread, the original poster used a July 2010 calendar and managed to find a complete Knight's Tour on which the 2nd, 6th, 11th, and 23rd moves landed on the dates of the 2nd, 6th, 11th, and 23rd respectively. Not surprisingly, it was Jaap of Jaap's Puzzle Page who found an 8-match solution.

I filed this in the back of my mind, but never really did anything until I ran across the Solving the Knight’s Tour on and off the Chess Board post which I mentioned last week. I liked the basic idea of being able to input a shape, and have the computer work out the tour, and especially the idea of using it to work out the XKCD forum's calendar challenge.

With a little knowledge of Java and graph theory under my belt, I managed to work out a program to solve it. For my fellow Java programmers, here's the main portion of my program, and here's the KnightsTour class I wrote to support it. Most of the hard work is done by lines 590 to 749. Those and lines 20 to 23 can removed if you're interested more in the general Knight's Tour than the particulars of the calendar challenge.

One of the first things I did, not surprisingly, was to find out how many day-to-move matches I could find in this month's calendar. I also found 8, all of which are highlighted below in red:

Yes, I've gone through every possible calendar, starting on every possible date, and learned quite a few interesting things in the process:

• Due to the fact that the number of days in a week (7) is odd, and the fact that the knight always moves an odd number of spaces (3), this means that a Knight on a calendar will always move from an odd date to an even date, and vice versa (just like what your teacher taught you about adding even and odd numbers). This, in turn, means that it's impossible to get ANY date matches if move #1 begins on an even-numbered date, as all the odd moves will land on even dates, and vice-versa.

• The above fact also means that if you start on an even date in a month with an odd number of days (29 or 31), you won't be able to complete a Knight's Tour.

• Yes, Jaap's 8-match path is the best one possible for July 2010 in particular. It also happens to be the only way to get 8 date-to-move matches in a Knight's Tour of a 31-day month beginning on a Thursday.

• Given any random month and year, you can always find a complete Knight's Tour and at least 6 date-to-move matches. Surprisingly, these minimum matches aren't found in the shortest months, as you may expect. With 30- and 31-day months starting on a Saturday, as well as 31-day months beginning on a Friday, 6 is the highest number of date-to-move matches you'll be able to find.

• There are months with 9 date-to-move matches, but none with more than that. 9 date-to-move matches can be found in a 29-, 30-, or 31-day month starting on a Tuesday or a Wednesday. In a 29-day month starting on a Thursday, or a 31-day month starting on a Monday, you can also find 9 date-to-move matches. You can often find more than 1 way to get to these matches, as well.

As it happens, next month (October 2014) is a 31-day month starting on a Wednesday, and here's one of the 3 possible ways to get 9 date-to-move matches:

I chose this one simply for the elegance of the column containing 16-23-30 and the diagonal containing 12-20-28. I also find it interesting that so many powers of 2 have date-to-move matches (2-4-8-16).

For the more math-inclined geeks, I'll wind this post up with all the maximum number of matches I've found, including the dates on which they start:

28-day months, starting on:
Sunday:    7 matches, beginning from the 1st or 23rd
Monday:    7 matches, beginning from the 1st or 21st
Tuesday:   8 matches, beginning from the 25th
Wedneday:  8 matches, beginning from the 1st
Thursday:  8 matches, beginning from the 1st or 5th
Friday:    8 matches, beginning from the 1st or 15th
Saturday:  7 matches, beginning from the 23rd or 25th

29-day months, starting on:
Sunday:    7 matches, beginning from the 1st
Monday:    7 matches, beginning from the 1st or 27th
Tuesday:   9 matches, beginning from the 25th
Wedneday:  9 matches, beginning from the 1st or 11th
Thursday:  9 matches, beginning from the 1st
Friday:    7 matches, beginning from the 1st, 5th, 27th, or 29th
Saturday:  7 matches, beginning from the 1st

30-day months, starting on:
Sunday:    7 matches, beginning from the 7th or 23rd
Monday:    8 matches, beginning from the 27th
Tuesday:   9 matches, beginning from the 25th
Wedneday:  9 matches, beginning from the 11th
Thursday:  8 matches, beginning from the 1st
Friday:    7 matches, beginning from the 1st or 7th
Saturday:  6 matches, beginning from the 1st or 25th

31-day months, starting on:
Sunday:    8 matches, beginning from the 23rd
Monday:    9 matches, beginning from the 7th or 31st
Tuesday:   9 matches, beginning from the 1st, 23rd, or 25th
Wedneday:  9 matches, beginning from the 7th
Thursday:  8 matches, beginning from the 5th
Friday:    6 matches, beginning from the 1st, 5th, 7th, or 31st
Saturday:  6 matches, beginning from the 1st, 23rd, 29th, or 31st


More Quick Snippets

Published on Sunday, September 07, 2014 in , , , , , , , ,

Luc Viatour's plasma lamp pictureSince I've changed my posting schedule, I seem to have neglected my monthly snippet posts!

Not to worry, however, as we're kicking off September with a good round-up of different takes on some of my favorite mental feats.

• One of the longest-standing tutorials on Grey Matters is the classic Knight's Tour. The traditional version usually happens on an 8 by 8 chessboard. What about other irregular, non-rectangular shapes?

Over at the Wolfram Blog, Jon McLoone explored that question using Mathematica in his post Solving the Knight’s Tour on and off the Chess Board. If you're interested in the programming and the math, there's plenty in this article. Even if you don't care for all the math and programming, the variety of boards with successful Knight's Tours is amazing and amusing. Who knew Pac-Man could play the Knight's Tour so well?

• Over in the Mental Gym, I have a full tutorial on squaring 2-digit numbers in your head. I've often wanted to move on to squaring 3-digit numbers, but never really found a method that suited me. However, I recently ran across a video tutorial from Mind Math called Mental Math Trick to Square 3-digit Numbers for Faster Calculation. It breaks the problem up into 2 steps, working with the hundreds digit followed by the remaining 2 digits as a group. If you're used to squaring 2-digit numbers, this method isn't difficult to learn and adapt:

• Back in March, I wrote a post about calculating powers of e in your head. At the time, I was unaware of Colin Beveridge's post, Secrets of the Mathematical Ninja: Estimating Powers of e, which featured a quicker, yet less accurate estimate.

After seeing my post, Colin took it upon himself to develop an improved method, which he posted as Powers of e Revisited: Secrets of the Mathematical Ninja. When you're done exploring those posts, check out the rest of Colin's Blog!

• Another favorite blog topic of mine is calendars. Beyond the standard day of the week for any date feat, there's plenty of interesting mathematical patterns and shortcuts waiting to be discovered in the calendar. One of the best round-ups I've found on the internet is P.K. Srinivasan's Number Fun with A Calendar (PDF version). Besides the PDF version, there's a zipped .DOC version and even a video demonstration of some of the topics from the book:

That's all for this month. I hope you found these enjoyable and useful!


Review: The Knight's Tour: A Scenic Journey

Published on Sunday, August 31, 2014 in , , , ,

Mbdortmund's chess knight photoOne of my favorite mental challenges, as many regular Grey Matters readers know, is the Knight's Tour. The challenge is, using only the chess knight's L-shaped move, to land on each of the 64 squares once.

Mentalist Richard Paddon recently released a download resource titled The Knight's Tour: A Scenic Journey. In this post, I'll take a close look at this new take on a classic feat.

We'll start with a quick peek at Richard Paddon himself performing the Knight's Tour, via the teaser ad:

The Knight's Tour: A Scenic Journey comes as a set of 3 files: A 45-page PDF of the same title, a 16-minute MPEG file of Paddon's performance, and the Knight's Tour Windows application used by Paddon, and programmed by Dave Everett.

In the PDF, right away, the author emphasizes the importance of developing drama in the Knight's Tour presentation. The first parts of the actual instruction, however, focus on developing the path through the board. Much of this part of the book may be familiar to readers of the “Knight's Tour” section of Paul Brook's Chrysalis Of A Polymath. However, Richard Paddon does add some new and helpful notes, such as the section on what he has dubbed “delta values”, which are familiar to those who have programmed a Knight's Tour, but little discussed in the use of performances.

In the next half of the book, Paddon discusses the presentational details. He starts with the benefits of the Knight's Tour, including its uncommon nature, and its huge potential on an emotional and theatrical scale. The thoughts behind the presentations are well laid out. Even if you disagree with any aspect of the presentation as written, you at least have a good starting point of why particular choices were made.

One of the more interesting choices is ending on a selected square, as seen in the above video. As the board empties, the chosen square becomes a more and more important focus, and becomes a natural point of building tension. The PDF winds up with a detailed description of how to use the program.

There are very few weaknesses in this product overall. One of the one that stands out to me as both a programmer and a blogger of mental feats was the choice of the Comic Sans font for the numbering of the board. If you're taking as much care as this author does to make an impact on the audience, there's probably better ways to label your board than a font designed specifically to have a comic-book appearance. On an equally minor note, the lightning in many of the shots of the performance video could be better. The importance of the video is for a more complete understanding of the presentation, so this isn't a huge drawback.

Overall, this is an excellent value for anyone seriously interested in performing the Knight's Tour. The basics of working through the path may be easily accessed in multiple sources, but the depth of knowledge that is presented, as well as the use of multiple media to demonstrate this make this the most complete lessons about all aspects of the Knight's Tour and its proper performance.

It's available for only $9.95 over at Lybrary.com and is a remarkably great value for that money. If the Knight's Tour interests you, Richard Paddon's The Knight's Tour: A Scenic Journey is a must-read.


New Mental Gym Tutorial: Easter Dates

Published on Sunday, August 24, 2014 in , , , , , , ,

DafneCholet's Calendar* photoPeople are often confused as to why the dates of Easter moves around so much from year to year. It moves so much much because Easter is the first Sunday after the first full moon after the first day of spring.

If this sounds confusing on its own, consider that the Roman Catholic and Eastern Orthodox churches use different calendars, which can yield different dates as a result!

Thanks to the work of John Conway, though, it is possible to work out the date of both Roman Catholic and Orthodox Easters in your head!

Some basic understanding and practice are all that's really needed to be able to calculate the Easter date in your head for any year from 1900 to 2099. In order to help make everything clearer, I've posted my new Easter Date For A Given Year tutorial over in the Mental Gym. To make it easier to learn, the tutorial is broken up into several steps:

The introduction explains the rules for Easter calculation in detail, as well as what you need to know to get started.

• The next section explains how to calculate the date of the traditional Roman Catholic Easter. After learning how to work out the date of the Paschal full moon (the first full moon after the first day of spring in a given year), you then learn how to work out the date of Easter for that same year.

• If you want to impress others by performing this feat, there's an entire section of presentation tips that can help make this feat entertaining.

• The method for calculating the date of Orthodox Easter is covered another section, as well. Assuming you can work out Roman Catholic Easter, there are surprisingly few changes involved in working out the Orthodox Easter date.

• Finally, there's another section for those adventuresome souls who want to venture on and work out Easter dates in other centuries. Here you can find out what changes need to be made to the original calculations.

Since practice is important, I've also developed a set of interactive Easter date quizzes. Since you work through each section verbally in a step-by-step manner, the quizzes work the same way. In the first quiz, you simply work out the paschal full moon date for Roman Catholic Easter. In the next quiz, you're asked about the paschal full moon and Easter dates. The Orthodox quizzes are similar, and start with the Roman Catholic dates first, since you need that information as a starting point.

If you put in a little understanding, a little practice, and a little time, you may surprise yourself (and others) with an impressive new skill!


Getting Squared Away

Published on Sunday, August 17, 2014 in , , , ,

Stefan Friedrich Birkner's square number imageOne of the more popular Mental Gym tutorials, probably because it's short and simple, is the Squaring 2-Digit Numbers Mentally tutorial.

Playing around with the methods in the math section of that tutorial, and doing a little research, I've run across an interesting pattern that make the calculations even simpler.

I'd noticed a pattern in some of the squares concerning their last two digits, but never really thought about the possibilities until I ran across this page about squares.

I've reproduced a slightly modified version of the number arrangement from that page below, but with the last two digits of each square highlighted. Although it's not shown here, the 2-digit pattern does continue on forever.

As I mention in the original tutorial, memorizing the squares of the numbers 1 through 25 is the most basic starting point, as is knowing how to square 2-digit numbers ending in 5. From here, though, we can take advantage of the pattern above in a different way.

SQUARING NUMBERS 26-50: When asked to square a number from 26-50, take the distance from 25 to that number, and multiply it by 100. Next, square the distance from the given to number to 50, and add it to the previous number you calculated. Those 2 steps give you the square.

For example, let's square 27. 27 - 25 = 2, so you multiply 2 × 100 = 200. The distance from 27 to 50 is 23, which you should know by heart as 529. Add 200 + 529 = 729, and you've got the answer to 27 squared!

How about, say, 38? How far is that from 25? Yes, it's 13, so we start with 1300. How far is 38 from 50? It's 12, and 12 squared is 144. 1300 + 144 = 1444, so we know 38 squared is 1444!

This approach makes numbers in the 40s almost ridiculously easy to square. You just say their distance from 25, then their distance from 50 squared. For 42, which is 25 + 17, you'd say, “17...” then square 8 (the distance from 42 to 50) and say, "..64!" With a little practice, numbers in the 40s almost square themselves!

SQUARING NUMBERS 51-75: As I mentioned above, the squares of the numbers beyond 50 continue with this pattern. Here are the squares of the numbers from 51 to 75, and here are just the last digits of each of those numbers.

The method for squaring these numbers is slightly different. After you're given the number, work out its distance from 50, add 25 to that distance, then multiply by 100. The final step is to square the distance from 50 to the given number, and add that to your previous calculation.

Let's use 56 as our first example. 56 - 50 = 6, so we add 6 + 25 = 31, and multiply by 100 to get 3100. 56, as we've already worked out is 6 away from 50, so we square 6 to get 36. 3100 + 36 = 3136, which is 56 squared! Notice that the 50s almost multiply themselves, just like the 40s did above!

Can you handle, say, 67 squared? That's 17 away from 50, so we work out 17 + 25 = 42, and 42 × 100 = 4200. Next, 17 squared is 289 (you know that from memory, right?), so we add 4200 + 289 = 4489!

SQUARING NUMBERS BEYOND 75: Squaring the numbers from 76 up to 125 can be handled just as in the original tutorial. You'll probably understand why this approach works more completely after seeing the pattern above.

Perhaps you can work out a method for numbers beyond 125? It can be done, but it's more than a minor variation on the above patterns.


Mind Your...Mental Math!

Published on Sunday, August 10, 2014 in , , , ,

Cover of Infinite Tower ebookPresh Talwalkar's Mind Your Decisions blog, has many interesting posts, some of which I've covered before.

I was thrilled recently when he began to make a series of videos about various mental math techniques!

It seemed to start about 2 months ago, when he posted the following video about squaring numbers ending in 5:

At the same time, he posted a companion video explaining why this trick worked:

Apparently, they've proved popular, as he's released a small series of them so far! Just like the above pair, each lesson provides a video teaching the method and an explanation behind the method. This is a good approach, as some may just want to impress their friends and family with a technique, without worrying about why it works, can just learn and go, while those who are more curious can take the extra step in learning about it.

Among the more unusual methods taught is the following method for squaring 34, 334, 3334, etc. and 67, 667, 6667 (explanation video):

A more standard technique is taught in this video about multiplying any 2 numbers between 11 and 19 (explanation video):

Presh Talwalkar has also made several short mental math videos that each teach simple techniques and includes simple explanations along the way. The first of these was a video on the rule of 72, a way of calculating how long it will take an investment to double:

Another one was this handy lesson in calculating percentages in your head:

My favorite of this group, however, is the following video on converting decimal numbers to binary in your head, as I've managed to impress even well-posted computer programmers with this feat:

If you enjoyed these videos, take a look around the rest of the Mind Your Decisions blog. Presh posts math puzzles every Monday, game theory posts every Tuesday, and other posts as thing grab his interest.


Mandelbrot Set: What Exactly Are We Looking At, Anyway?

Published on Sunday, August 03, 2014 in , , ,

Wolfgang Beyer's Mandelbrot set renderingPictures of the Mandelbrot set, such as the one to the left, are pretty to look at, and fascinating when you zoom in to see more detail.

But the origin of the design often isn't made clear. In this post, I'm going to slowly step through each important detail in way that helps you understand it.

Recently, Numberphile posted a video about the Mandelbrot set, as explained by Dr. Holly Krieger of MIT:

Even this video tends to gloss over some points, so my explanation will be somewhat slower, and build up differently.


Let's start with something very familiar, the number line you probably grew up seeing in your elementary classroom every day.

Martin Smith-Martinez' number line image
We're also going to start with a very simple formula: z2 + c. The variable c will act as a chosen starting point, and we'll be putting different numbers in the formula, except that c will remain constant (c is for constant).

What about that z2, though? That, of course, represents z multiplied by itself, and we'll be changing the value of z. Where do we start? As in the video, the starting point for z will always be 0. The next value for z, though, is whatever we get out of the equation from the previous calculation.

One of the simplest starting point is 1, so let's demonstrate with that. Since we chose 1, the formula becomes z2 + 1. Using 0 for our initial value of z, we have 02 + 1 = 0 + 1 = 1. If we take this 1 and use it as our new value of z, and keep using the previous result for our new value of z, we get the following values:

  • 12 + 1 = 1 + 1 = 2
  • 22 + 1 = 4 + 1 = 5
  • 52 + 1 = 25 + 1 = 26
  • 262 + 1 = 676 + 1 = 677
You can, of course, continue doing this as long as you like.

Each of these repeated calculations is referred to as an iteration of the formula. Perhaps not surprisingly, these numbers get bigger quickly after only a few iterations. We can have Wolfram|Alpha run through the z2 + 1 formula for us. Click on the More button in the Values pod will show that after only 9 iterations, the number is already up to about 1.94727 × 1045 (roughly 2 followed by 45 zeroes)!


What's the big deal? Doesn't every number get bigger? No, not all of them do. One of the more interesting numbers that doesn't get bigger is -2. If we run z2 + (-2) through a few iterations, it quickly reaches a result of +2 and never gets any bigger!

If we use a number that's even slightly smaller than -2, such as -2.000001, we can see that such numbers will continue to grow. That's why the 2 cases in the video are defined as Case One: Blows Up and Case Two: Stays Small (<= 2), and why 2 is considered a special value in the Mandelbrot set.

Now, in the video, Dr. Krieger mentions that 14 is on the boundary, so what happens with that number itself? Not only does 14 NOT surpass 2, it never even reaches 0.5!

So, what we have so far is just a line from 2 to about 14. Why about? Well, 14 isn't as solid a border as -2. For example, we can move a tiny bit to the right on the number line, say to 100001400000, and we find that point never exceeds 2. That point is too small to accurate mark on the number line, as compared to the next handy fraction, such as 13, which eventually does grow past 2.


Let's finally get off the number line and jump into 2 dimensions. We could attempt to use standard graph paper-style Cartesian coordinates of the form (a, b), but the mathematics required to handle 2 separate coordinates quickly complicates the formula.

This is why the imaginary number plane and complex numbers come into the picture. Read BetterExplained.com's A Visual, Intuitive Guide to Imaginary Numbers to get a good grasp of how these work. If those interest you, you may want to read Intuitive Arithmetic With Complex Numbers and Understanding Why Complex Multiplication Works at the same website.

For c, let's try the complex set of coordinates 0.5 + 0.5i. Running those coordinates through Wolfram|Alpha we see that after only 14 iterations, the results become roughly (-6×10287) + (-4×10287i)!

Thanks to the effects of i, the results can obviously get into negative numbers quickly, and the answers get confusing. What we need to do, then, is translate each result into polar coordinates. We're not so much worried about θ (the angle), but rather r (the radius), which is measured as the distance from the origin point. The radius is always a positive number, and we can simply judge whether this is bigger than 2.

Converting (-6×10287) + (-4×10287i) to polar coordinates, we get a radius of roughly 7.2111×10287 units from the center, so these coordinate definitely escape 2!

To cover two dimensions, we need to focus on a particular range. In the video, Dr. Krieger talks about using a radius of 2 units in all directions, but most of the Mandelbrot pictures you see tend to use a range of -2 to +1 on the real number line, and i to -i on the imaginary plane.

Besides a range, we also need to choose a “resolution.” To keep things simple, we might choose a resolution such as 70×30. So, we'd break up the space from -2 to +1 into 70 equally-spaced coordinates horizontally, and we'd break up the space from i to -i into 30 equally-spaced coordinates vertically.

Then, for each of those 2100 (70 × 30) coordinate pairs, we'd put them in complex coordinate form (a + bi), and assign that to c. We'd run through z2 + c for that set of coordinates and see if the radius ever became larger than 2 (in other words, whether there's a limit to the iterations). If so, we would assign a white square to it. If not, we would assign a black square to it (or an asterisk, if we're working in ascii).

Mapping those results gives you an image that appears as follows (click the image to see a larger version):

Elphaba's ascii Mandelbrot rendering
This picture is the result of 2100 calculations, with each calculation being iterated to varying degrees. Is it any wonder than the Mandelbrot set couldn't have been discovered until computers became commonplace?

Now things are starting to look much more familiar! For a better picture, just as you would with any display, you increase the resolution. Given 300×220 as the resolution, you would get an even clearer picture (click the image to see a larger version):

Connelly's hi-res b&w Mandelbrot rendering


Those simple black and white versions only show which sets of complex coordinates, when iterated through z2 + c, fall into which of the 2 cases. The pictures you usually see are much more colorful. What is the deal with those pictures?

Instead of asking just a yes-or-no question (Does the radius of the iteration ever exceed 2?), we change the question to “How long before the radius of the iteration exceeds 2?” If the radius of the iteration never exceeds 2, we use black. If the radius of the iteration exceeds 2 after 1 iteration, we'll use a color we'll call color 1, after 2 iterations we use a 2nd color, after 3 iterations we use a 3rd color, and so on.

That approach, known as the escape time algorithm, gives us the standard Mandelbrot set images with which you are likely familiar (click the image to see a larger version):

Wolfgang Beyer's colored Mandelbrot set rendering
Notice that you even get better contrast with this version, as you can see “branches” that aren't easily seen in the black-and-white versions.

As an aside, that name, escape time algorithm, brings up a good point. In the Numberphile video above, they make it sound as if distance is important. Instead, it's actually the amount of iterations it takes a number to escape the value of 2. The Mandelbrot isn't a measurement of distance, but rather time.

The colors chosen are usually a matter of personal preference, which is why you see so many different variations. If you don't like the banding effect of sudden color changes, there are even ways to smooth that out.

Remember how it's impossible to tell when moving the tiniest amount to the right of 14 on the number line would result in a set of iterations whose radius would ever exceed 2? Thanks to computers, we can choose a smaller range, an appropriate resolution, and zoom in to study the complexity of that particular area (known to Mandelbrot set fans as “Elephant Valley”):

Consider that all these results have been coming from iterating the same equation, z2 + c. What happens if we try taking z to another power, such as z3 + c or z4 + c? Here's what happens when changing those powers from 2 to 5:

Alex Tav's Mandelbrot animation for z to powers from 2 to 5
Once you understand the basics, there's plenty of ways to explore the amazing world of fractals such as these. I've written on fractals several times on Grey Matters, including Iteration, Feedback, and Change: Fractals, R.I.P. Benoît Mandelbrot (November 20, 1924 - October 14, 2010), and A Closer Look, so you can explore further if you wish.