The sudoku package provides an environment for typesetting sudoku grids. A sudoku puzzle is a 9x9 grid where some of the squares in the grid contain numbers. The rules are simple: every column can only contain the digits 1 to 9, every row can only contain the digits 1 to 9 and every 3x3 box can only contain the digits 1 to 9. More information, including help and example puzzles, can be found at sudoku.org.uk. This site also has blank sudoku grids (or worksheets), but you will not need to print them from there if you have this package installed.