Sudoku, a logic-based, combinatorial number-placement puzzle where the objective is to filll a 9 x 9 grid with digits so that each column, each row, and each of the nine 3 x 3 subgrids that compose the grid contains all of the digits from 1 to 9. It was originally called Number Place, it has appeared since 1979 in puzzle books but it only began to gain widespread popularity in 1986 when a Japanese puzzle company published it under the name Sudoku, meaning “single number”.