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3, 3, 6, 18, 72, 360, 2160, 15120, 120960, 1088640, 10886400, 119750400, 1437004800, 18681062400, 261534873600, 3923023104000, 62768369664000, 1067062284288000, 19207121117184000, 364935301226496000, 7298706024529920000, 153272826515128320000
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OFFSET
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0,1
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COMMENTS
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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
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LINKS
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FORMULA
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E.g.f.: 3/(1-x).
a(n) = n*a(n-1), with a(0) = 3.
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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); # Zerinvary Lajos, Dec 22 2008
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MATHEMATICA
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PROG
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(Sage) [3*factorial(n) for n in range(25)] # G. C. Greubel, May 05 2019
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CROSSREFS
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Row 13 of A276955 (from term a(3)=18 onward).
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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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STATUS
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approved
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