Calcudoku

How to play Calcudoku

Calcudoku is a number puzzle that mixes Sudoku with simple sums. The board is a square grid: 4×4, 6×6 or 7×7. Thick lines split it into groups of squares called cages. Each cage has a small clue in its corner, made of a target number and a sign, such as 12× or 3−.

Goal

Fill every square with a number from 1 up to the size of the grid. Each number must appear exactly once in every row and every column. The numbers in each cage must reach the cage's target with its sign:

• + the numbers add up to the target.
• × the numbers multiply to the target.
• − (two squares) the bigger number minus the smaller one gives the target.
• ÷ (two squares) the bigger number divided by the smaller one gives the target.
• A cage of one square shows its number with no sign. Just write it in.

Numbers may repeat inside a cage, as long as they are not in the same row or column. Each puzzle here has exactly one answer.

Step by step

1. Pick a square with a tap or a click, or move with the arrow keys. Its cage, row and column light up.
2. Enter a number with the pad under the grid or with the number keys.
3. Turn on Notes (or press N) to keep small pencil marks of the numbers that could fit.
4. Use Erase or Backspace to clear a square, and Undo to take back a step.
5. A repeated number turns red. When a cage is full but misses its target, its clue turns red. A correct cage fades its clue.

Levels

Easy is 4×4. Medium is 6×6 with bigger cages. Hard is 7×7 with large cages and few single squares. Easy and Medium puzzles can always be solved with logic alone.

End of the game

The puzzle is done when every square is correct. The timer stops and shows your time. Your game is saved in this browser. For a similar challenge, try Kakuro.

Strategy tips

• Fill single squares first. A cage of one square gives you its number for free, and that number is then blocked in its row and column.
• Big products narrow things down. On a 6×6 grid, 2 squares with 30× can only be 5 and 6. Look for targets with only one way to make them.
• Use the row total. Every row adds up to the same number (21 on a 6×6 grid). If you know all cages in a row but one square, you can work out the last one.
• Watch for division. A 2÷ cage on a 4×4 grid must be 1 and 2 or 2 and 4. Write both pairs in your notes.
• Think about 1s. A × cage with a small target often holds a 1. A − cage with a target one less than the grid size must be 1 and the top number.
• Notes save time. On Hard, note every option for the big cages and remove them as rows fill up.