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Search: id:A052503
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| A052503 |
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Number of permutations sigma without fixed point such that sigma^4=Id. |
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+0
1
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| 1, 1, 9, 105, 2625, 76545, 3440745, 176080905, 12034447425, 922995698625, 87505195602825
(list; graph; listen)
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OFFSET
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0,3
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 28
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FORMULA
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E.g.f.: exp(1/2*x^2+1/4*x^4)
Recurrence: {a(1)=0, a(0)=1, a(2)=1, a(3)=0, (-11*n-6-n^3-6*n^2)*a(n)+(-n-3)*a(n+2)+a(n+4)}
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MAPLE
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spec := [S, {S=Set(Union(Cycle(Z, card=2), Cycle(Z, card=4)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A081461 A110698 A012485 this_sequence A122569 A039619 A080505
Adjacent sequences: A052500 A052501 A052502 this_sequence A052504 A052505 A052506
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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