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A052577 a(n) = (3^(n+1)-1)*n!/2. 1
1, 4, 26, 240, 2904, 43680, 786960, 16531200, 396789120, 10713669120, 321413702400, 10606692096000, 381841394457600, 14891820610867200, 625456552834713600, 28145546185236480000, 1350986237814140928000, 68900298484208615424000, 3720616124549638938624000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..18.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 520

FORMULA

E.g.f.: 1/(-1+x)/(-1+3*x).

Recurrence: {a(0)=1, a(1)=4, (3*n^2+9*n+6)*a(n)+(-4*n-8)*a(n+1)+a(n+2)=0.}.

a(n) = (-1/2+1/2*3^(n+1))*n!.

MAPLE

spec := [S, {S=Prod(Sequence(Z), Sequence(Union(Z, Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);

CROSSREFS

Sequence in context: A304338 A115416 A302606 * A203935 A210912 A210913

Adjacent sequences:  A052574 A052575 A052576 * A052578 A052579 A052580

KEYWORD

easy,nonn

AUTHOR

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

STATUS

approved

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Last modified July 25 21:44 EDT 2021. Contains 346294 sequences. (Running on oeis4.)