Sudoku

Sudoku (数独 sūdoku) (English pronunciation: /suːˈdoʊkuː/ soo-DOH-koo) is a logic-based, combinatorial number-placement puzzle. The objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 sub-grids that compose the grid (also called "boxes", "blocks", "regions", or "sub-squares") contains all of the digits from 1 to 9. (Wikipedia Article on Sudoku)