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A006070
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Number of Hamiltonian paths on n-cube which are strictly not cycles.
(Formerly M5295)
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7
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OFFSET
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1,3
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COMMENTS
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Number of Gray codes of length n which strictly do not close.
More precisely, this is the number of ways of making a list of the 2^n nodes of the n-cube, with a distinguished starting position and a direction, such that each node is adjacent to the previous one and the last node is not adjacent to the first.
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REFERENCES
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M. Gardner, Knotted Doughnuts and Other Mathematical Entertainments. Freeman, NY, 1986, p. 24.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Table of n, a(n) for n=1..5.
Eric Weisstein's World of Mathematics, Hypercube Graph
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EXAMPLE
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There are no such paths for n=1 or n=2 (the square). For n = 3 every path has to end at the node of the cube that is diametrically opposite to the start. There are 16 choices for the start and for each start there are 3 Hamiltonian paths that end at the opposite node, so a(3) = 3*16 = 48.
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CROSSREFS
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Cf. A006069, A091299.
Sequence in context: A159441 A011787 A292516 * A081262 A340186 A238001
Adjacent sequences: A006067 A006068 A006069 * A006071 A006072 A006073
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane.
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EXTENSIONS
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a(5) from Greg Barton (greg_barton(AT)yahoo.com), May 24 2004
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STATUS
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approved
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