A234009 Free polyominoes with 4n squares, having 90-degree rotational symmetry about a square corner.

1, 1, 4, 10, 35, 114, 403, 1432, 5239, 19271, 71820, 269417, 1017920, 3864879

Offset: 1

Author

John Mason, Dec 18 2013

Keywords

• nonn
• hard
• more

Comments

The number of free polyominoes of size 4n that have 90-degree rotational symmetry about a point that coincides with the corner of a square, independently of any other symmetries. Note that for polyominoes which have a hole in the center, the center of rotation will be the corner of a square within the hole, rather than being the corner of a square of the polyomino itself. The sequence is defined for 4n rather than n as polyominoes of size not multiple of 4 cannot have the required symmetry.

Crossrefs

Cf. A000105, A001933, A234006, A234007, A234008, A234010.

Extensions

a(8)-a(14) from John Mason, Dec 13 2021