Sudoku is a numbers puzzle. It does not require any math, though. In fact, if we replace numbers with letters, shapes, or even colors - the puzzle won't change.
...
We've carefully crafted all our Sudoku puzzles to ensure that each of them is interesting to solve, no matter what level of difficulty you prefer.
...
Sudoku Mood was designed with simplicity in mind. Our goal is to make sure that users will be able to fully enjoy our website right after they see it for the first time.