6 is the smallest perfect number.

This post probably belongs at uselessconcepts.com as well.  Those crazy jerks.

This site is a list of quite a few numbers from 0 to 9999.  Each number has its own special characteristic. 

For example:

24 is the largest number divisible by all numbers less than its square root.
200 is the smallest number which can not be made prime by changing one of its digits.
3645 is the maximum determinant of a 12 x 12 matrix of 0's and 1's.
4080 = 17P3.
7647 is a Keith number.
7663 is the product of two primes which are reverses of each other.
9988 is the number of prime knots with 13 crossings.

I don't get this one at all:

89 = 81 + 92

I have no clue what many of the terms mean.  But I am sure it is useful to someone.