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Search: id:A112676
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| A112676 |
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Number of Hamiltonian cycles on a triangular grid, n vertices on each side. |
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+0
2
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OFFSET
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1,4
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COMMENT
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This sequence counts cycles in a triangular region of the familiar 2-dimensional lattice in which each point has 6 neighbors (sometimes called either the "triangular" or the "hexagonal" lattice), visiting every vertex of the region exactly once and returning to the starting vertex. Cycles differing only in orientation or starting point are not considered distinct.
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EXAMPLE
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a(3) = 1, the only Hamilton cycle being the obvious one running around the edge of the triangle.
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CROSSREFS
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Cf. A003763, A112675.
Adjacent sequences: A112673 A112674 A112675 this_sequence A112677 A112678 A112679
Sequence in context: A049088 A089041 A059511 this_sequence A103112 A064941 A112612
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KEYWORD
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more,nonn
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AUTHOR
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Gareth McCaughan (gareth.mccaughan(AT)pobox.com), Dec 30 2005
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