Fill in the grid with digits from 1 to 9 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 at a cell reveals the value chooser. Click at the selected value changes the state of the cell. More details about grid control are at the help page.