Imagine having someone think of a number from 1 to 100, having them cube the number using a calculator, telling you only the result, and you're able to calculate the cube root of their result (the original number they put in the calculator)!

Learning to work out cube roots of perfect cube is an impressive feat, but it's far less difficult than it appears.

We'll get right to the method, taught in the video below. You can read the MindYourDecisions.coom post New Video – Calculate Cube Roots In Your Head for further details.



Over in the Mental Gym, I have a more detailed tutorial on working out cube roots of perfect cubes, including a cube root quiz.

Back in March of 2013, Scam School also taught the cube root feat in their own unique way. If you like this feat and want to take it a step further, check out Numberphile's fifth root feat tutorial. Surprisingly, this is even easier than the cube root feat!

5 years ago today, I created Grey Matters and put up its first post!

Let's take a look back first at each of the previous blogiversaries;
1st Blogiversary
2nd Blogiversary
3rd Blogiversary
4th Blogiversary

Please, take this opportunity to look through the site, and possibly discover something you didn't know before. After 5 years, this site has more to offer than it may appear at first glance. Start with perhaps the menu just under the logo, the featured content, or the navigation over in the rightmost column.

If you've gone through at least the blogiversary posts, then you've noticed we're big on Pi here at Grey Matters (just under 10% of the posts here have dealt with Pi in some way), which is why the blog was purposely started on Pi Day (and why I post as Pi Guy).

Update: On another blog, I've posted some goodies to celebrate both Pi Day and Albert Einstein's birthday.

Since there's so much celebrating going on, how about a special Pi Day magic trick? It's courtesy of James Grime and Brian Brushwood, and is happening on Twitter.

Now, believe it or not, even I have recently been created a twitter account, and you can follow me on Twitter here. If you want to be part of a real world record attempt, here's what you have to do to be part of it:



Rumor has it that the method to this will be revealed in a special edition of Scam School, scheduled to be posted later on tonight.

Speaking of Pi, and 5-year spans, many of us Pi fans are waiting for the “big one”, 5 years from now. On that day, Pi Day will fall on 3/14/15! A once-in-a-century chance to celebrate the ultimate Pi Day!

Are you doing anything to celebrate? Did you take part in the Pi Day Magic Trick? Perhaps you just have good blogiversary wishes for Grey Matters? Let's hear about it in the comments!

Do you want some March snippets? If so, here they are!

• In the previous edition of Snippets, I reported on Memgellan (iTunes Link), an iPhone/iPod Touch app that helps you arrange journeys for the Journey System of memory.

Since then, I've found 2 apps that help with using the Major/Peg System. The first is Your Memory Coach (iTunes Link), which teaches you the basics of the major system, helps you set up your own keywords, and quizzes you on them. The other app is NumberThink (iTunes Link), which is more of a reference that can both help you learn how to form words from any number, and numbers from any word.

• Ben Pridmore, who won the 2009 World Memory Championships, has no problem sharing the particular memory systems he uses to win. On this memory consulting page he describes his system briefly, while it's described in more detail on this archived page. You can see video of Ben Pridmore in action at last year's memory championships here, and describing how he memorized multiple decks of cards here. Follow Ben Pridmore's own blog here.

• For a while, I've had Robert H. Nutt's book How To Remember Names and Faces available on my online store for $19.95. If want to learn to remember names and faces, but you'd like it for a lower price and/or prefer a digital copy, your wish is my command! It's now available at Lybrary.com for $12 in downloadable PDF format!

• I just recently visited a Learning is Fun store for the first time. While there, I picked up some days and months signs that should help add a visual punch to the Day of the Week For Any Date feat.

I also found an interesting product called Mathematical Curiosities, which is basically 4 mathematical magc trick. There's 5 dice which work in the same manner as the prices in Mental Shopper, a version of the classic Age Cards, a numerical version of Dan Harlan's Missing Think, and 4 addition bars which are perfect for the Dicipher Bars routine from Docc Hilford's Book Of Numbers Volume Two (Qebhsennuf).

• Next Sunday, besides being Pi Day and Grey Matters' 5th blogiversary (can you believe it?), it's also the occasion for a special Pi Day magic trick on Twitter! James Grime, known to many of you as singingbanana, gives the details in the video below. You can find out more about this at http://pidaymagic.com, http://twitter.com/jamesgrime, and http://twitter.com/shwood.

Believe it or not, I haven't covered all the mathematical visualization sites on the web yet.

When you talk about hundreds and thousands of anything, it's somewhat easy to visualize. When you start talking about millions, billions and beyond, then it becomes harder to relate and understand. We'll start with an introduction to the concept by the Fat Boys:

How about visualizing time? How long was a million seconds, minutes or hours ago? How about a billion? How about a trillion? Over at How much is a Million? A Billion?, you can get an idea of just how long ago that was. Keep in mind that this site was posted in 2000, so at this writing, one million hours ago would be the year 1892, not 1885.

If you're curious about going all the way up to 1 nonillion (1,000,000,000,000,000,000,000,000,000,000) and beyond, this site uses paper folding to get the idea across. Just to keep you grounded, most pieces of paper can't be folded in half more than 7 times, although Britney Gallivan has folded a piece of paper in half 12 times.

Usually when you're talking about millions, billions and beyond, you're talking about money. Thanks to the MegaPenny Project, you can see how big various amounts up to 1 quintillion pennies appear. If cows are more your thing, you can see a similar visualization at the MegaMoo project.

Now that we can more easily visualize millions of dollars, how about actually having millions of dollars to spend? That would be nice, so why not try the lottery? Well, this lottery simulation (Java required) can show you why not very quickly. It simulate your average lottery, in which you pick 6 different numbers out of 50, but it goes farther than that. It assumes that you play $1 each week, and keeps track not only of your wins and losses, but what you would have if you invested that dollar in a savings account at 5% interest. After just a year or two, the difference is already shocking. Let it run for 20 years, and you'll be in awe of the amounts involved (but you can visualize them in pennies!).

Back in the original Visualizing Pi post, I mentioned various versions of the Powers of 10 concept. The most detailed version I found of this would have to be Nikon's Universcale page (Flash required). Like the previous versions, it zooms in and out, but there is more detailed descriptions as you cross the various size boundaries. You can stop and examine each item in detail, as well. There's not much instruction required to use this site. Just run your mouse over just about anything on the screen, drag to change speed and direction, and click anything that is highlighted.

For my millions and billions of readers (hey, I can dream, right?), this should be plenty to explore until next time. My next post should be up about 350,000 seconds after this one.

Ever seen a 200 digit number? For those who haven't, here's one:

85,877,066,894,718,045,602,549,144,850,158,599,202,771,247,748,960,878,023,151,390,314,284,284,465,842,798,373,290,242,826,571,823,153,045,030,300,932,591,615,405,929,429,773,640,895,967,991,430,381,763,526,613,357,308,674,592,650,724,521,841,103,664,923,661,204,223

Imagine being given that number and then being asked to find a number that, when multiplied by itself 13 times, will give that number as an answer (in other words, the 13th root). Oh, and you have less than 90 seconds!

That was the task set for Alexis Lemaire on July 24th of this year, and he did it in only 77.99 seconds at Oxford's Museum of the History of Science!

Back in 2004, Lemaire also set a record for finding the 13th root of a 100-digit number in only 3.62 seconds!

How does someone even begin to calculate a 13th root? The best way is to work up to the task slowly. The best place to start is to learn how to do cube roots. This gives you an idea of some of the processes and abilities needed to perform mental root calculations.

From there, you can work up to fifth roots, and then to square roots. Yes, it is strange that square roots are trickier to mentally calculate than 3rd or 5th roots, but that is indeed the case.

Once you're familiar with those, you can start working on 13th roots themselves. A knowledge and understanding of logarithms will be of great help here.

In case you've been wondering, I'll wrap up by ending the suspense. The 13th root of the aforementioned 200-digit number is 2396232838850303.

Here are some quick snippets for you:

* Neuroscientists from UCSF and Standford have created a site called Lumosity that is designed to improve your attention, processing speed and memory. This is done over the course of thirty 15-minute sessions which require registration, which is free while the site is still in beta. You can also evaluate your IQ for free without registering.

* Computer clusters from three different institutions have found the prime factors of a 307-digit number after 11 months of computing. while this may not sound like much more than computers solving a boring math problem, it becomes interesting when you realize that this technique can be used to break advanced encryption techniques used by businesses and governments. Granted, 11 months of computing is a long time, but as processors get faster, this will fall.

* Cinema Advanced offers a wonderful alternative to rote script memorization in their post, Don't Memorize Your Lines.

* If you need to do some real-world estimates for varying types of problems, mental math shortcuts provides just what it promises.

* If you enjoyed the Prisoner's Dilemma post, you might also enjoy the Toilet Seat Dilemma, where similar game theory is applied to the age-old question of leaving the toilet seat up.

The new Guinness World Record for reciting Pi from memory is now 67890 digits! It was set by Lu Chao from China. The record was set on November 19th, 2005, but was only just recently confirmed by Guinness.

At this writing, Akira Haraguchi's attempt at 100,000 digits has neither been confirmed nor denied by Guinness, so we may see Lu Chao's record broken in the coming months.

Last year, I mentioned Akira Haraguchi, who recited 83,431 digits of Pi from memory. He has just bested his own personal record, and may be the new world record holder for reciting the most memorized digits of Pi, if his claim is verified by Guinness World Records.

Akira Haraguchi has recited 100,000 digits of Pi from memory, and has submitted the video of his recitation to Guinness for verification. He started at 9 AM (Japan Time) on October 3rd, 2006. Passing his previous record of 83,431 digits at about 10:30 PM that night, he finished this amazing feat at 1:28 AM the following morning!

For those interested in memorizing Pi, you can start with the basics, and quickly learn 400 digits of Pi! 400 digits is, at this writing, enough to put you among the top 50 memorizers in the world, according to the Pi World Ranking List.

Do you want to set a record, but don't think you can beat 100,000 digits? Try going for a record in your city, state or country. For example, the North American Pi memorization and recitation record is “only” 10,980 digits.

Back in March, I briefly mentioned Gaurav Rajav's attempt at the North American Pi Record. He was promised a new Xbox and a game he wanted, if he broke the record. He didn't break the record during that attempt, so his parents are reported to have bought him the Xbox without the game.

In a new attempt, however, Gaurav Rajav has now broken the 27-year-old North American Pi Record! His new Pi memorization record stands at a remarkable 10,980 digits, and there are now only 8 people in the entire world who have memorized more digits than him.

I'm guessing this means that he finally received the Xbox game he wanted?

Gaurav Rajav, 15-year-old, managed to recite Pi to 8,784 digits, in an attempt to go for the 10,790-digit US record. There's more detail on this story over at Yahoo News.

The world record for reciting Pi was broken today. Akira Haraguchi recited Pi to 83,431 digits, almost doubling Hiroyuki Goto's 42,195-digit record.

If you would like to try your hand at remembering Pi, check out Memorizing Pi to 400 Decimal Places and Mentat Wiki's PiMemorisation article for a good start.