Mathdoku (Same as KENKEN) is an instruction-free Puzzle for training the brain. As in Sudoku, the goal of each puzzle is to fill a grid with digits –– 1 through 3 for a 3×3 grid, 1 through 5 for a 5×5, 1 through 6 for a 6×6, etc. –– so that no digit appears more than once in any row or any column. Grids range in size from 3×3 to 9×9.