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Search: id:A000704
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| A000704 |
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Number of degree-n even permutations of order dividing 2.
(Formerly M3511 N1427)
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+0
13
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| 1, 1, 1, 1, 4, 16, 46, 106, 316, 1324, 5356, 18316, 63856, 272416, 1264264, 5409496, 22302736, 101343376, 507711376, 2495918224, 11798364736, 58074029056
(list; graph; listen)
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OFFSET
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0,5
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COMMENT
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Number of odd 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.
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LINKS
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T. D. Noe, Table of n, a(n) for n=0..200
A. M. Goyt, Avoidance of partitions of a 3-element set
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FORMULA
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E.g.f.: e^x cosh ( x^2 / 2 ).
a(n) = sum[i=0,floor(n/4), C(n,4i)*(4i)!! ]. - Ralf Stephan, May 08 2007
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CROSSREFS
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Adjacent sequences: A000701 A000702 A000703 this_sequence A000705 A000706 A000707
Sequence in context: A054498 A134139 A097125 this_sequence A007315 A055342 A050616
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KEYWORD
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nonn,easy
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AUTHOR
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njas and J. H. Conway (conway(AT)math.princeton.edu)
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