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A361288
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Number of free polyominoes of size 2n for which there exists at least one closed path that passes through each square exactly once.
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1
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1, 1, 3, 6, 25, 84, 397, 1855, 9708, 51684, 286011, 1609097, 9222409, 53543338, 314612803
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OFFSET
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2,3
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COMMENTS
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A polyomino for which more than one closed path exists counts as 1. On the other hand, in A266549, distinct closed paths count separately. For example for n=7, this latter sequence distinguishes between
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+ +-+ +-+
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and
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+ +-+ +-+
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+-+ +-+-+
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LINKS
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EXAMPLE
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For n = 4 the a(4) = 3 solutions are:
XXX XX XXXX
X X XXX XXXX
XXX XXX
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CROSSREFS
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Cf. A266549 (where distinct closed paths count separately).
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KEYWORD
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nonn,more,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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