Sudoku: Fun in a number of ways. Popular Japanese puzzle game using a 9 by 9 grid divided into 9 more grids of 3 by 3. The object is to fill each column using the numbers 1 to 9 using each number only once per row, horizontal and vertical. In addition, each number must only appear once in any given 3 by 3 grid. For the solution to this puzzle, look for the button titled, Puzzle Solution.