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A137191
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Number of n-celled polyiamonds with perimeter < n+2.
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0
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0, 0, 0, 0, 0, 1, 1, 4, 11, 39, 120, 403, 1254, 4000, 12475, 39030
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OFFSET
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1,8
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COMMENTS
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These are n-cell polyiamonds with the perimeter less than the maximum possible one.
If we associate a graph to a polyiamond with vertices representing cells and edges representing two cells with a common edge, then this sequence enumerates polyiamonds whose corresponding graphs have cycles.
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LINKS
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FORMULA
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CROSSREFS
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KEYWORD
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hard,more,nonn
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AUTHOR
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STATUS
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approved
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