As in Sudoku, the goal of each puzzle is to fill a grid with digits
— 1 through 4 for a 4×4 grid, 1 through 5 for a 5×5 grid, etc. —
so that no digit appears more than once in any row or any column.
Additionally, Mathdoku grids are divided into heavily outlined groups of
cells called “cages”, where the numbers in the cells of each cage
must produce a certain “target” number when combined using a specified mathematical
operation (either addition, subtraction, multiplication or division).
Digits may be repeated within a cage, as long as they are not in the same row or column. The target number and operation appear in the upper left-hand corner of the cage.
— Source: Wikipedia