

A234009


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


5




OFFSET

1,3


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.


LINKS

Table of n, a(n) for n=1..7.


CROSSREFS

Cf. A000105, A001933, A234006, A234007, A234008, A234010.
Sequence in context: A283070 A222631 A030003 * A198324 A149175 A149176
Adjacent sequences: A234006 A234007 A234008 * A234010 A234011 A234012


KEYWORD

nonn,hard,more


AUTHOR

John Mason, Dec 18 2013


STATUS

approved



