addition to the tiling problems described above, there are recreational mathematics puzzles that require folding a polyomino to create other shapes. Gardner proposed several simple games with a set of free pentominoes and a chessboard. Some variants of the Sudoku puzzle use nonomino-shaped regions on the grid. The video game Tetris is based on the seven one-sided tetrominoes (spelled "Tetriminos" in the game), and the board game Blokus uses all of the free polyominoes up to pentominoes. Etymology The word polyomino and the names of the various orders of polyomino are all back-formations from the word domino, a common game piece consisting of two squares, with the first letter d- fancifully interpreted as a version of the prefix di- meaning "two." The name domino for the game piece is believed to come from the spotted masquerade garment domino, from Latin dominus. Most of the numerical prefixes are Greek. Polyominoes of order 9 and 11 more often take the Latin prefixes nona- (nonomino) and undeca- (undecomino) than the Greek prefixes ennea- (enneomino) and hendeca- (hendecomino). See also Percolation theory, the mathematical study of random subsets of integer grids. The finite connected components of these subsets form polyominoes. Young diagram, a special kind of polyomino used in number theory to describe integer partitions and in group theory and applications in mathematical physics to describe representations of the symmetric group. Blokus, a board game using polyominoes. Squaregraph, a kind of undirected graph including as a special case the graphs of vertices and edges of polyominoes. Notes External links Karl Dahlke's polyomino finite-rectangle tilings An implementation and description of Jensen's method A paper describing modern estimates (PS) MathPages – Notes on enumeration of polyominoes with various symmetries List of dissection problems in Fairy Chess Review Tetrads by Karl Scherer, Wolfram Demonstrations Project. Polyforms Recreational mathematics Mathematical games