Write a number in every blank square of the grid. When the grid is full, every orthogonally connected group of identical numbers should have an area equal to that number: so 1s always appear alone, 2s in pairs, and so on.
To place a number, click the mouse in a blank square to select it, then type the number you want on the keyboard. You can also drag to select multiple squares, and then type a number to place it in all of them. To erase numbers, select one or more squares in the same way and then press Backspace.
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