Calcudoku on the full 9 by 9 grid mixes Sudoku with a little arithmetic. There are no boxes. Instead, heavy lines divide the grid into cages, and the small number in the corner of each cage is the total its numbers must add up to. Every row and column holds each number from 1 to 9 once. Easy is the free daily Calcudoku, and members will be able to play Medium and Hard as well.