A polyomino of the fifth order; five connected squares.

The twelve pentominoes are:

X  XX  X   X   XX  XX  XXX  XXX  XX   XX    X   XX
X  X   XX  X   XX  X   X     X    XX   XX  XXX   X
X  X   X   XX  X   XX  X     X     X   X    X    XX
X  X   X    X
These twelve shapes are the subject of many tiling puzzles and other recreational mathematics. The most well-known tiling problem involving these shapes is the tiling of a rectangle using each pentomino once. Because their total area is 60, several rectangles are possible: 3x20, 4x15, 5x12, 6x10.
If text formatting isn't helping, the pentomino pieces are named after their shapes. F I L N P T U V W X Y Z. They represent all possible ways five squares can be set edge to edge.

There are 2339 unique ways to fit the twelve pieces into a 6x10 rectangle. There are only two ways to fit them into a 3x20 rectangle, and they're closely related.

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