A pseudo-polyomino, also called a polyking, polyplet or hinged polyomino, is a plane geometric figure formed by joining one or more equal squares edge to edge or corner to corner at 90°. It is a polyform with square cells. The polyominoes are a subset of the polykings.
Enumeration of polykings
Free, one-sided, and fixed polykings
There are three common ways of distinguishing polyominoes and polykings for enumeration:
- free polykings are distinct when none is a rigid transformation (translation, rotation, reflection or glide reflection) of another (pieces that can be picked up and flipped over).
- one-sided polykings are distinct when none is a translation or rotation of another (pieces that cannot be flipped over).
- fixed polykings are distinct when none is a translation of another (pieces that can be neither flipped nor rotated).
The following table shows the numbers of polykings of various types with n cells.