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 A234009 Free polyominoes with 4n squares, having 90-degree rotational symmetry about a square corner. 5
 1, 1, 4, 10, 35, 114, 403, 1432, 5239, 19271, 71820, 269417, 1017920, 3864879 (list; graph; refs; listen; history; text; internal format)
 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..14. CROSSREFS Cf. A000105, A001933, A234006, A234007, A234008, A234010. Sequence in context: A030003 A339845 A363465 * 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

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Last modified September 24 17:02 EDT 2023. Contains 365579 sequences. (Running on oeis4.)