Normal sudoku rules apply (1-9 in each row, column, and box). Multi-digit numbers read left-to-right and top-to-bottom.
Purple dash = 2-digit prime number. Green square = 2-digit square number.
Red cross = not prime or square. No symbol = can be anything. (prime, square or not)
Press BACKSPACE to delete, and SHIFT to toggle the highlight. Right-click for rays.