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Catculus
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About the game
Catculus is a number puzzle with a simple rule. A grid of tiles, each with a digit on it, sits on the left, and a target number sits on the right. Your job is to pick tiles that touch each other, in any shape, and make their digits add up to exactly that target. A group that hits it scores points and a new target comes up.
Overshoot, and you lose a bit of your life bar. Lose it too many times and the game ends, so careful sums matter more than fast clicks. To keep it from turning into plain arithmetic, black cats hop onto the board and cover tiles, hiding the digits. You have to remember what was under each cat or take a guess and live with the result.
Every so often you are offered a bonus to pick, and these can change how the game scores by quite a lot: a bigger multiplier, a different way to build the sum, more room for mistakes. A string of good groups builds a multiplier, so a careful run can climb high on the score.
Antti Haavikko made Catculus for js13kGames 2025, where the whole game, zipped, had to fit in 13 kilobytes. The theme that year was Black Cat.
Playing it here
Click Play to start. Click a tile to select it, then click neighbouring tiles to add them to the group. The running sum is shown at the bottom, next to the target. When it matches, the group is cashed in on its own. Click a selected tile again to drop it from the group. The game is drawn in widescreen, so on a tall window you will see bars above and below it. Nothing is saved: each visit starts a new game.
Controls
| Input | Action |
|---|---|
| Click / tap on a tile | select it and add it to the group |
| Click / tap on a selected tile | drop it from the group |
| Click / tap on a bonus | choose it |
A few things worth knowing
Start from big digits. A 9 or an 8 has few partners that fit, so use them while you can still see the whole board.
Remember the cats. When a cat sits on a tile, note the digit before it disappears. Re-using that memory is where most of the score comes from.
Mind the multiplier. The multiplier grows with a streak, so a single wrong guess costs more than just a life.
Credits and licence
Catculus was developed by Antti Haavikko for js13kGames 2025 and released under the MIT licence. The licence text, together with the notices for the ZzFX and SoundBox sound code that plays the effects and music, is linked from this page, and the source code is on GitHub.