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A052666 E.g.f. 1/(1-x-3x^2). 0
1, 1, 8, 42, 456, 4800, 69840, 1093680, 20482560, 420577920, 9736070400, 245887488000, 6806133734400, 203555082931200, 6565920180019200, 226728504946944000, 8355118608764928000, 327047476385710080000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

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

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 613

FORMULA

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

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

Sum(1/13*(1+6*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+3*_Z^2))*n!

a(n) = n!*A006130(n). - R. J. Mathar, Nov 27 2011

MAPLE

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

CROSSREFS

Sequence in context: A316283 A236328 A284337 * A065789 A025064 A241695

Adjacent sequences:  A052663 A052664 A052665 * A052667 A052668 A052669

KEYWORD

easy,nonn

AUTHOR

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

STATUS

approved

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Last modified July 5 17:29 EDT 2020. Contains 335473 sequences. (Running on oeis4.)