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Search: id:A052560
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| 3, 3, 6, 18, 72, 360, 2160, 15120, 120960, 1088640, 10886400, 119750400, 1437004800, 18681062400, 261534873600, 3923023104000, 62768369664000, 1067062284288000, 19207121117184000, 364935301226496000
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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a(n) is the size of the centralizer of a 3-cycle in the symmetric group S_(n+3). - Ahmed Fares (ahmedfares(AT)my-deja.com), May 12 2001
3 times factorial numbers. [From Omar E. Pol (info(AT)polprimos.com), Jan 17 2009]
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 502
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FORMULA
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E.g.f.: -3/(-1+x)
Recurrence: {(-1-n)*a(n)+a(n+1), a(0)=3}
For n>0: a(n) = SUM(A083746(k): 1<=k<=n+1). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 14 2007
a(n) = A000142(n)*3. [From Omar E. Pol (info(AT)polprimos.com), Jan 17 2009]
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MAPLE
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spec := [S, {S=Union(Sequence(Z), Sequence(Z), Sequence(Z))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
a:=n->sum(n!, k=1..n):seq(a(n)-sum(n!, k=4..n), n=0...19); # [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 22 2008]
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CROSSREFS
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Cf. A129380.
Cf. A000142. [From Omar E. Pol (info(AT)polprimos.com), Jan 17 2009]
Sequence in context: A132818 A134068 A025256 this_sequence A147836 A019235 A103895
Adjacent sequences: A052557 A052558 A052559 this_sequence A052561 A052562 A052563
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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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