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Drag from 1. Drag back, tap a square on the line, or right-click to go back to the last number.

How to play

Start on 1 and draw a line through neighbouring squares, not diagonally.
Pass the numbers in order: 1, 2, 3 and so on, ending on the highest number.
Fill every square exactly once.
Undo reverses your last move. Right-click cuts the line back to the last number it passed.
On a keyboard, click the board and use the arrow keys. Ctrl+Z undoes.