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Search: id:A052811
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| A052811 |
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A simple grammar: sequences of pairs of cycles. |
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+0
2
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| 1, 0, 2, 6, 46, 340, 3308, 36288, 460752, 6551424, 103685232, 1803956880, 34247483664, 704301934752, 15598712592864, 370149922235520, 9369093828260736, 251968378971718656, 7174943434198029312
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Stirling transform of (-1)^n*a(n)=[0,2,-6,46,-340,...] is A005359(n)=[0,2,0,24,0,...]. - Michael Somos Mar 04 2004
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 775
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FORMULA
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a(n) = (-1)^n*Sum_{k=0..floor(n/2)} Stirling1(n, 2*k)*(2*k)!. - Vladeta Jovovic (vladeta(AT)Eunet.yu), Sep 22 2003
E.g.f.: 1/(1-log(1-x)^2).
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MAPLE
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spec := [S, {B=Cycle(Z), C=Prod(B, B), S=Sequence(C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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PROGRAM
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(PARI) a(n)=if(n<0, 0, n!*polcoeff(1/(1-log(1-x)^2), n))
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CROSSREFS
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Sequence in context: A058925 A136557 A092662 this_sequence A078603 A001587 A078537
Adjacent sequences: A052808 A052809 A052810 this_sequence A052812 A052813 A052814
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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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