Sudoku

Four difficulties, from easy to expert. Every puzzle is generated with a single solution that can be reached by logic alone. You will never need to guess and back out of a dead end.

Notes mode lets you pencil in candidates, and any digit that clashes with the same row, column or box is flagged straight away so a mistake does not survive twenty moves.

The keypad sits under the board for a thumb, and a keyboard types digits straight in. Undo walks back through your moves, the clock runs while you think, and the squares still to fill are counted for you. A daily sudoku arrives at midnight, the same grid for everybody in the world, with its own streak on this device.