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A052646 E.g.f. 1/((1-x)(1-x-x^2)). 0
1, 2, 8, 42, 288, 2400, 23760, 272160, 3548160, 51891840, 841881600, 15008716800, 291711974400, 6139842508800, 139136552755200, 3377722892544000, 87457261731840000, 2405869763641344000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..17.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 592

FORMULA

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

Recurrence: {a(0)=1, a(1)=2, a(2)=8, (n^3+6*n^2+11*n+6)*a(n)+(-2*n-6)*a(n+2)+a(n+3)=0}

(-1+Sum(1/5*(4+3*_alpha)*_alpha^(-1-n), _alpha =RootOf(-1+_Z+_Z^2)))*n!

n!*Sum(k=0, n, A000045(n+1)).

a(n) = n!*A000071(n+3). - R. J. Mathar, Nov 27 2011

MAPLE

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

MATHEMATICA

With[{nn=20}, CoefficientList[Series[1/((1-x)(1-x-x^2)), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Dec 01 2018 *)

CROSSREFS

Sequence in context: A324961 A078592 A225108 * A320343 A002856 A093461

Adjacent sequences:  A052643 A052644 A052645 * A052647 A052648 A052649

KEYWORD

easy,nonn

AUTHOR

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

STATUS

approved

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Last modified November 14 12:44 EST 2019. Contains 329116 sequences. (Running on oeis4.)