Sudoku's arithmetic cousin. Every cage must hit its target.
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Fill the grid so every row and every column contains each number from 1 to the grid size exactly once — the Sudoku rule. On top of that, the outlined blocks, called cages, each carry a target and an operation. The numbers in a cage must combine to give the target.
Cages of one cell are free answers. Cages using subtraction or division can be taken in either order, so a 2÷ cage might be 2 and 1, or 4 and 2, or 6 and 3. That ambiguity is the source of most of the difficulty.
This version: Nine cells, a friendly start. Your best score is saved in this browser, so you can come back and try to beat it. Nothing is uploaded and no sign-up is needed.
Sudoku gives you starting numbers and no arithmetic. Calcudoku gives you almost no starting numbers but adds arithmetic constraints, so you deduce from the sums rather than from what is already placed.
Tetsuya Miyamoto, a Japanese maths teacher, created it in 2004 as a teaching tool. He called it KenKen, meaning roughly 'cleverness squared'.
Single-cell cages, then cages where the target is only achievable one way — a 12× cage of two cells in a 4×4 grid must be 3 and 4.