1. # Mathematical Curio

If you take any integer and rearrange the digits however you like, the difference between the original number and the rearranged number will always be divisible by 9.

For example:

number = 12345
rearranged = 43215
difference = 43215 - 12345 = 30870
difference / 9 = 3430


More generally, you can do the same with numbers ...