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Search: id:A001465
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| A001465 |
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Number of degree-n odd permutations of order 2.
(Formerly M2538 N1003)
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+0
6
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| 0, 0, 1, 3, 6, 10, 30, 126, 448, 1296, 4140, 17380, 76296, 296088, 1126216, 4940040, 23904000, 110455936, 489602448, 2313783216, 11960299360, 61878663840, 309644323296, 1587272962528, 8699800221696, 48793502304000
(list; graph; listen)
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OFFSET
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0,4
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COMMENT
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Number of even partitions of an n-element set avoiding the pattern 123 (see Goyt paper). - Ralf Stephan, May 08 2007
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REFERENCES
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L. Moser and M. Wyman, On solutions of x^d = 1 in symmetric groups, Canad. J. Math., 7 (1955), 159-168.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
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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A. M. Goyt, Avoidance of partitions of a 3-element set
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FORMULA
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a(n) = sum[i=0,floor((n-2)/4), C(n,4i+2)*(4i+2)!! ]. - Ralf Stephan, May 08 2007
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CROSSREFS
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Sequence in context: A109490 A130760 A154134 this_sequence A094276 A151376 A066245
Adjacent sequences: A001462 A001463 A001464 this_sequence A001466 A001467 A001468
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com) and J. H. Conway (conway(AT)math.princeton.edu)
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EXTENSIONS
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More terms from Pab Ter (pabrlos(AT)yahoo.com), May 11 2004
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