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A217595
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Number of free n-celled polyominoes without holes and odd side lengths.
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1
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1, 0, 1, 1, 2, 4, 7, 12, 35, 55, 144, 335, 710, 1791, 4195
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OFFSET
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1,5
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COMMENTS
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If you checkerboard color the vertices of the square lattice, a(n) is the number of orthogonal polygons of area n, which alternates between white and black vertices.
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LINKS
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EXAMPLE
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For n=5 the a(5)=2 pentominoes are 'I' and 'X'.
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CROSSREFS
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KEYWORD
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nonn,hard,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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