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A052573 (1+3^n)*n!. 0
2, 4, 20, 168, 1968, 29280, 525600, 11027520, 264579840, 7142929920, 214280640000, 7071181286400, 254561568307200, 9927888709939200, 416971151460864000, 18763699200390144000, 900657519773147136000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Table of n, a(n) for n=0..16.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 516

FORMULA

E.g.f.: -2*(-1+2*x)/(-1+x)/(-1+3*x)

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

(1+3^n)*n!

MAPLE

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

MATHEMATICA

With[{nn=20}, CoefficientList[Series[-2(-1+2x)/(-1+x)/(-1+3x), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Jul 04 2021 *)

CROSSREFS

Sequence in context: A303671 A330663 A102087 * A110371 A120388 A061348

Adjacent sequences:  A052570 A052571 A052572 * A052574 A052575 A052576

KEYWORD

easy,nonn

AUTHOR

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

STATUS

approved

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Last modified September 20 11:38 EDT 2021. Contains 347584 sequences. (Running on oeis4.)