Crazy math.

Take any number and rearrange its digits to form another number.

Subtract one from the other. The difference will always be divisible by 9.

Stolen from The Futility Closet

It's true as far as I can tell (of course to be fair you cant use 1-9, and some numbers like 11, 22, 33, ect. wont work because 11-11 is 0 (unless you count 0 as being a number))

8731 - 8317 = 414 / 9 = 46
627184 - 482617 = 144567 / 9 = 16063
92873 - 73892 = 18981 / 9 = 2109
10 - 01 = 9 / 9 =1
92 -29 = 63 / 9 = 7
981 - 189 = 792 / 9 =88

Weird