MathDoku is yet another interesting Sudoku variant.
The games at MathDoku are is loosely similar to killer Sudoku and based on the same rules of Kenken, an educational puzzle invented by Tetsuya Miyamoto in Japan. MathDoku games go by a number of names including KenKen, KenDoKu, kenduko, cancan, square wisdom, minuplu, calcudoku, Math Sudoku and latincalc. It is also slightly similar to a crossword or jigsaw puzzle since it requires trial and error to solve.
MathDoku features games in 4×4, 6×6, and 8×8 tables and each have difficulties ranging from easy, medium, hard, and no-op (a version that hides the math operation). At the MathDoku website you can play this highly addicting logic and math puzzle game. It is available in both online and printable formats for free. Happy Puzzling!
Update : Mathdoku is also available for the iPhone and called Sudoku Math.