Calcu-doku & Sudoku : Every sudoku fan knows that this popular number puzzle has always flirted with math. But the two have never come togetherâ¦until now! Meet Calcu-doku, the newest and sure to be hottest development in the sudoku world. All that's needed is simple arithmetic, so even solvers who aren't mathematically inclined will have fun. Each puzzle looks like a normal sudoku, except for sectioned-off smaller areas that contain a little math symbol and a number. For example, let's say that two numbers are boxed in with a â21xâ in the corner: that means they multiply to 21, so they must be either 3/7 or 7/3. All the other traditional sudoku rules remain in place, but the added variety of a little touch of math makes Calcu-doku extra-addictive. Plus: 144 regular sudoku, too!