Sudoku is the classic logic-based, combinatorial number-placement puzzle. If you've been off-planet since 1986 you may not know the objective: fill an N×N grid with digits (1 to N) such that each row, column and block contain only one occurrence of each available digit. (Some squares are pre-filled as clues; place the rest of the digits correctly until the grid is complete).
This Lite version of the game has 8 modes of play and is available on all your iOS devices. All puzzles are auto-generated; so you'll never need to buy another puzzle book (or make an in-app-purchase).