Oh, I see, Soduku doesn't even involve adding. I didn't realize that. I see why Alex said "no math!"
But if you do want some math, it's apparently all about combinatorics and permutation group theory. Here's one place to start learning about Soduku math...
http://en.wikipedia.org/wiki/Mathematics_of_Sudoku
And this is a cute article:
The mathematics of Sudoku, a puzzle that boasts "No math required!".