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 A052560 a(n) = 3*n!. 12
 3, 3, 6, 18, 72, 360, 2160, 15120, 120960, 1088640, 10886400, 119750400, 1437004800, 18681062400, 261534873600, 3923023104000, 62768369664000, 1067062284288000, 19207121117184000, 364935301226496000, 7298706024529920000, 153272826515128320000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS 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. - Omar E. Pol, Jan 17 2009 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 502 Luis Manuel Rivera, Integer sequences and k-commuting permutations, arXiv:1406.3081 [math.CO], 2014. FORMULA E.g.f.: 3/(1-x). a(n) = n*a(n-1), with a(0) = 3. For n>0: a(n) = Sum_{k=1..n+1} A083746(k). - Reinhard Zumkeller, Apr 14 2007 MAPLE 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 MATHEMATICA 3*Range[0, 25]! (* Vladimir Joseph Stephan Orlovsky, Jun 12 2011 *) PROG (MAGMA) [3*Factorial(n): n in [0..25]]; // Vincenzo Librandi, Jun 13 2011 (PARI) a(n)=3*n! \\ Charles R Greathouse IV, Nov 20 2011 (Sage) [3*factorial(n) for n in range(25)] # G. C. Greubel, May 05 2019 CROSSREFS Cf. A000142, A129380. Row 13 of A276955 (from term a(3)=18 onward). Sequence in context: A132818 A134068 A025256 * A147836 A284710 A019235 Adjacent sequences:  A052557 A052558 A052559 * A052561 A052562 A052563 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified November 25 14:15 EST 2020. Contains 338623 sequences. (Running on oeis4.)