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Search: id:A003091
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| A003091 |
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[ 2^{n(n-1)/2} / n! ].
(Formerly M1870)
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+0
1
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| 1, 1, 1, 2, 8, 45, 416, 6657, 189372, 9695869, 902597327, 154043277297, 48535481831642, 28400190511772276, 31020581422991798557, 63530150754287203445810, 244912468225468597942626507, 1783398168624923337196441201196, 24605638395579573858211783276124626
(list; graph; listen)
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OFFSET
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1,4
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 246.
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MAPLE
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A003091:n->floor(2^(n*(n-1)/2)/n!);
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CROSSREFS
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Sequence in context: A009345 A084553 A144164 this_sequence A119501 A006664 A141117
Adjacent sequences: A003088 A003089 A003090 this_sequence A003092 A003093 A003094
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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