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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 (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 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

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Last modified December 18 12:06 EST 2018. Contains 318229 sequences. (Running on oeis4.)