Normal sudoku rules apply, and the marked diagonals each contain 1-9, as do the blue cells. The Little Killer Clue shows the sum of the indicated diagonal. Box 3 (red) is a Magic Square. All the rows, columns, and diagonals sum to the same number. Box 5 (green) uses all the numbers, 1-9 in forming 2-digit Prime Numbers reading across (left-to-right) or down. Box 9 (purple) contains all the 2-digit Square Numbers reading across (left-to-right) or down.