

A234009


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


5



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

1,3


COMMENTS

The number of free polyominoes of size 4n that have 90degree 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..14.


CROSSREFS

Cf. A000105, A001933, A234006, A234007, A234008, A234010.
Sequence in context: A222631 A030003 A339845 * A198324 A149175 A149176
Adjacent sequences: A234006 A234007 A234008 * A234010 A234011 A234012


KEYWORD

nonn,hard,more


AUTHOR

John Mason, Dec 18 2013


EXTENSIONS

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


STATUS

approved



