Hiku

Hiku is a calm number puzzle for people who like sudoku. Every number jumps exactly as many squares as it shows, across or up and down, and lands on another number. The smaller is taken from the larger, and equal numbers both vanish. Clear the board.

Every day there are four new boards, from easy to expert, and the same four for everyone. Play them right in the conversation: drag a number onto another, or tap one and then its target. First-time players get three short lessons. A gold ring marks a good place to start, and undo is always there.

Every board can be cleared; the challenge is finding the order. Ask for the rules, or for a hint on how to spot a trap, and the assistant explains without giving the solution away.

Hiku has no ads, no account and no timer, and stores nothing about you. It comes in English, Norwegian, Swedish, Danish, Finnish and German, and is also an app for iPhone and iPad.