This Sudoku variant consists of a 6 x 6 grid made up of 2 x 3 subgrids (called “regions”). Some cells already contain numbers. The goal is to fill the empty cells with one number each, so that each column, row, and region contains the numbers 1 through 6 exactly once. Each number in the solution thus occurs only once in each of the three “directions”, hence the “single numbers” implied by the name of the puzzle. This Sudoku variant is also particularly suitable for children or for Sudoku beginners.