

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.


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CROSSREFS



KEYWORD

nonn,hard,more


AUTHOR



EXTENSIONS



STATUS

approved



