# Cantor Expansion
Instead of using a base number, like binary or decimal, you can
use factorials to represent a number. This is called Cantor expansion.
10 = 1*3! + 2*2!
17 = 2*3! + 2*2! + 1*1!
n = sum{a_i * i!} where i=1,2,..., 0 <= a_i <= i.
Isn't it interesting? I found it on my first number theory book
when I was in high school.