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A351616
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Number of free polyominoes with 2n squares, having 180-degree rotational symmetry about a vertex of a square, and no other symmetry.
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2
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0, 0, 1, 2, 12, 43, 174, 657, 2571, 9911, 38633, 150437, 588544, 2306204, 9061179, 35665587, 140648710, 555514177, 2197298561, 8702439446, 34506900216, 136972867380, 544237912916, 2164377093376, 8614630304437
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OFFSET
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1,4
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COMMENTS
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The sequence enumerates a subset of the polyominoes enumerated by A006747.
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LINKS
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EXAMPLE
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a(3)=1 because of:
OOO
OOO
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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