value placement constraints, alternate symbols (e.g. letters), alternate mechanism for expressing the clues, and compositions with overlapping grids. See Sudoku – Variants for details and additional variants. Sudoku types and classes Sub Doku – Grids smaller than 9×9. Sometimes referred to as "Children's Sudoku" (especially the 4×4 variant) as the reduced number of possibilities makes them easier to solve. Super Doku – Grids larger than 9×9. Prime Doku – N×N grid where N is prime. Generally constructed with polyomino regions, e.g. Go Doku and pentominos. Maximum Su Doku – The class of puzzles which have the maximum number of independent clues needed to allow a complete and unique solution. Minimum Su Doku – The class of puzzles which have the minimum number of clues needed to allow a complete and unique solution, i.e. minimal Sudokus. Jigsaw Sudoku – Regular 9×9 Sudoku that row and column rules apply, but instead of a 3×3 grid they are nine Jigsaw shapes. Variants by size Polyomino – A shape composed of equal sized, side-adjacent squares. Often used for Sudoku region variants. Polyominos are named by size: (5) pentomino, (6) hexomino, (7) heptomino, (8) octomino, and (9) nonomino.Du-sum-oh – 5×5, 6×6, 7×7, 8×8 or 9×9 grid with irregular, polyomino, shaped regions and minimal number of clues. Du-Sum-Oh puzzles are also known as Latin Squares Puzzles (invented by Mark Thompson), Squiggly Sudoku, Jigsaw Sudoku, Irregular Sudoku, or Geometric Sudoku. These puzzles typically have anywhere from 5 to 9 rows. The number of rows is always equal to the number of columns. The regions are polyominos made of the same number of squares that are in any one row of the puzzle. The irregularity of the regions compensates for the relatively small number of givens.4×4 – Shi Doku. Four 2×2 regions. Shi is Japanese for 4.5×5 – Go Doku and Logi-5. A 5×5 grid with pentomino regions. Go is Japanese for 5.6×6 – Roku Doku A version of this was featured at the World Puzzle Championship. Six 2×3 rectangular regions.7×7 – (Unnamed). A 7×7 grid with six heptomino regions and a disjoint region, featured at the World Puzzle Championship.8×8 – Super Sudoku X. Four 4×2 + four 2×4 rectangular blocks.9×9 – Sudoku: Classic 9×9 grid.Sudoku X: Adds diagonals with uniqueness requirement. Jigsaw Sudoku: 9×9 grid with nonomino regions. 12×12 – Maxi. Twelve 3×4 rectangular blocks. 16×16 – Number Place Challenger. Sixteen 4×4 regions. 25×25 – Sudoku the