What's Special About This Number? If you know a distinctive fact about a number not listed here, please e-mail me. primes graphs digits sums of powers bases combinatorics powers/polygonal Fibonacci geometry repdigits algebra perfect/amicable pandigital matrices divisors games/puzzles 0 is the additive identity . 1 is the multiplicative identity . 2 is the only even prime . 3 is the number of spatial dimensions we live in. 4 is the smallest number of colors sufficient to color all planar maps. 5 is the number of Platonic solids . 6 is the smallest perfect number . 7 is the smallest number of sides of a regular polygon that is not constructible by straightedge and compass. 8 is the largest cube in the Fibonacci sequence . 9 is the maximum number of cubes that are needed to sum to any positive integer . 10 is the base of our number system. 11 is the largest known multiplicative persistence . 12 is the smallest abundant number . 13 is the number of Archimedian solids . 17 is the number of wallpaper groups .

The Thirty Greatest Mathematicians Click for a discussion of certain omissions. Please send me e-mail if you believe there's a major flaw in my rankings (or an error in any of the biographies). Obviously the relative ranks of, say Fibonacci and Ramanujan, will never satisfy everyone since the reasons for their "greatness" are different. I'm sure I've overlooked great mathematicians who obviously belong on this list. Please e-mail and tell me! Following are the top mathematicians in chronological (birth-year) order.

Nerd Paradise : Divisibility Rules for Arbitrary Divisors It's rather obvious when a number is divisible by 2 or 5, and some of you probably know how to tell if a number is divisible by 3, but it is possible to figure out the division 'rule' for any number. Here are the rules for 2 through 11... The last digit is divisible by 2. 25 Spectacular Movies You (Probably) Haven't Seen Midnight in Paris Woody Allen’s latest places starving writer Owen Wilson in Paris with his fiancée, Rachel McAdams. Searching for inspiration for his incomplete novel, Owen begins taking strolls around the city at night where he discovers an unexpected group of people. I wish I could be more specific, but it would ruin the surprise. Tanya Khovanova’s Math Blog » Blog Archive » Divisibility by 7 is a Walk on a Graph, by David Wilson My guest blogger is David Wilson, a fellow fan of sequences. It is a nice exercise to understand how this graph works. When you do, you will discover that you can use this graph to calculate the remainders of numbers modulo 7. Back to David Wilson: I have attached a picture of a graph. Write down a number n.

Weierstrass functions Weierstrass functions are famous for being continuous everywhere, but differentiable "nowhere". Here is an example of one: It is not hard to show that this series converges for all x. In fact, it is absolutely convergent.