1 "Frame Sudoku" (also known as "Outside Sum Sudoku") consists of an empty grid. Numbers in the outside frame equal the sum of the first three numbers in the corresponding row or column in the given direction.
11 In some sudokus main diagonals also contain the digits 1 through 9. This variant is called «Sudoku X» or «Diagonal Sudoku». Use the check box Diagonals for such sudokus.
21 Sudoku may contain additional four regions 3 x 3. This format was first introduced in the Dutch newspaper «NRC Handelsblad» by Peter Ritmeester. It is called «Windoku» («Four-Box Sudoku», «Hyper Sudoku»).
51 «Sudoku-DG» (also known as «Offset Sudoku») contains 9 disjoint groups in the puzzle, one for each relative box position. Each group has a distinct color. The group of 9 cells with the same color must also contain digits 1 through 9.
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