Domino (mathematics)


In mathematics, a domino is a polyomino of order 2, that is, a polygon in the plane made of two equal-sized squares connected edge-to-edge. When rotations and reflections are not considered to be distinct shapes, there is only one free domino.
Since it has reflection symmetry, it is also the only one-sided domino. When rotations are also considered distinct, there are two fixed dominoes: The second one can be created by rotating the one above by 90°.
In a wider sense, the term domino is sometimes understood to mean a tile of any shape.

Packing and tiling

Dominos can tile the plane in a countable infinity of ways. The number of tilings of a 2×n rectangle with dominoes is, the nth Fibonacci number.
Domino tilings figure in several celebrated problems, including the Aztec diamond problem In which large diamond-shaped regions have a number of tilings equal to a power of two, with most tilings appearing random within a central circular region and having a more regular structure outside of this "arctic circle", and the mutilated chessboard problem, in which removing two opposite corners from a chessboard makes it impossible to tile with dominoes.