Back in March 2007, as the movie The Number 23 was being released, I posted an entry about special properties of the number 23, and where to find properties of just about any number. These online “number museums” have . . . well, multiplied since then!

Among the number museums I initially mentioned were What's Special About This Number?, Number Gossip, and the Java-powered site, The Secret Lives of Numbers. To completely catch up with the original post, it should be noted that Notable Properties of Specific Numbers is still around, but it now has a new home.

Archimedes' Laboratory, a site I've mentioned many a time before, has their list, called the Zoo of Numbers. This number features unique and interesting facts for numbers as high as 715, and as low as “NaN”, which many computer programmers will recognize as the symbol for “Not a Number” They've even gone so far as to arrange for you to shop for items featuring your favorite number!

Compared to “Zoo of Numbers,” the Database of Number Correlations sounds much drier and stuffier. However, don't let that fool you, as this site features more detail than most of the other sites. They include not only mathematical properties, but films with that number in the title, famous lists of the given number, and even things that happened that year, if applicable! For example, the entry for number 9 not only discusses facts like 9 is a square number and that it's the sum of the first 3 odd numbers, but also brings up the 9 Christian fruits of the spirit, films like 9 1/2 Weeks, 9 Songs, and the Whole 9 Yards, and even the fact that Roman emperor Vespasian was born in 9 A.D.!

There's one such “number museum” that you've probably visited, yet never thought of it as such. Which site is this? I'm talking about the well-known Wikipedia, where you can find individual entries on a mind-boggling amount of integers! Wikipedia's editability by anyone makes this especially rich as a number-property resource. Where else could you learn bizarre number trivia such as, in the entry on number 8, that Michael Phelps won 8 of a possible 8 medals in the Olympic Games that began on 8/8/08, at exactly 8:08:08 PM local time? If you don't want to be limited to integers, look through the categories of rational numbers, real numbers, or any kind of numbers!

Just as in any field, collectors of number properties want their work to stand out by giving special focus to their work. A prime example of this is the Prime Curios! site. The only properties that this site will even consider listing for any given number must somehow relate to prime numbers. Take the humble number 42, for example. 42 itself is obviously not a prime number, yet it has the interesting prime properties such as being immediately between two primes, and being the total of the two least consecutive primes ending in 1 (11 + 31 = 42).

An even more impressive specialty can be found at The On-Line Encyclopedia of Integer Sequences. As the name suggests, it doesn't focus on individual numbers like all the sites above, but rather sequences of whole numbers. The one thing that makes this site incredibly useful is the fact that you can enter any integer sequence into their search engine, when then quickly provides all the entries of which that sequence could be a part. This site can really surprise you sometimes. If you search for the classic sequence 1, 1, 2, 3, 5, 8, 13, you might think that it would only return the entry on Fibonacci numbers. If so, you'll be surprised when it returns more than 80 different possible number sequences!

As you can see, The On-Line Encyclopedia of Integer Sequences is the perfect site If you ever wanted to cheat like crazy when challenged with things like Idiot World's Math Godeek Test or number sequence puzzles from Mental Floss' Brain Games column. Of course, any true math geek realizes that, given any sequence of numbers, the next number can be mathematically proven to be ANYTHING, if you employ polynomials!