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A052801
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A simple grammar: labeled pairs of sequences of cycles.
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1
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1, 2, 8, 46, 342, 3108, 33324, 411360, 5741856, 89379120, 1534623936, 28804923024, 586686138384, 12885385945248, 303537419684064, 7633673997722496, 204125888803996800, 5782960189212871680
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 759.
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FORMULA
| E.g.f.: 1/(-1+ln(-1/(-1+x)))^2
a(n) = Sum_{k=0..n} (-1)^(n-k)*Stirling1(n, k)*(k+1)!. - Vladeta Jovovic (vladeta(AT)eunet.rs), Sep 21 2003
a(n) = D^n(1/(1-x)^2) evaluated at x = 0, where D is the operator exp(x)*d/dx. Cf. A052811. - Peter Bala, Nov 25 2011
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MAPLE
| spec := [S, {C=Cycle(Z), B=Sequence(C), S=Prod(B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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PROG
| (Maxima) makelist(sum((-1)^(n-k)*stirling1(n, k)*(k+1)!, k, 0, n), n, 0, 17); [Bruno Berselli, May 25 2011]
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CROSSREFS
| Sequence in context: A088791 A111552 A128085 * A180390 A074599 A007289
Adjacent sequences: A052798 A052799 A052800 * A052802 A052803 A052804
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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