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
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved