Author: Dmitry Grishchenko
Fill in the grid with digits from 1 to N putting one digit per a cell. Each row, column and outlined area should contain every digit exactly once. Dots show all two-digit perfect square numbers reading from top to bottom or from left to right. Perfect squares numbers are 16, 25, 36, 49, 64, 81.
Grid control: Click the mouse button at the selected cell to change the filling of the cell. More details about grid control are at the help page.