A pentomino is a plane geometric figure formed by joining five equal squares edge to edge. It is a polyomino with five cells. There are twelve pentominoes, not counting rotations and reflections as distinct. They are used chiefly in recreational mathematics for puzzles and problems. Pentominoes were formally defined by American professor Solomon W...

Found on http://en.wikipedia.org/wiki/Pentomino

(from the article `number game`) ...A polyomino is a simply connected set of equal-sized squares, each joined to at least one other along an edge. The simpler polyomino shapes are ...

Found on http://www.britannica.com/eb/a-z/p/40

A five-square polyomino.

Found on http://www.daviddarling.info/encyclopedia/P/pentomino.html

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