Sukaku ("Suuji Kakure"; also known as "Pencilmark Sudoku") has 81 groups of digits in a 9 x 9 grid. Like a standard sudoku, the puzzle must be completed in such a way that each row, each column and each 3 x 3 box contains digits 1 through 9. Only the candidates shown in the grid can be used.
Task files have the extension *.SUK.