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A052669 E.g.f. (1-2x)/(1-3x-x^2+2x^3). 0
1, 1, 8, 66, 840, 12960, 242640, 5286960, 131765760, 3693755520, 115058361600, 3942342835200, 147360531225600, 5967185903078400, 260221271108198400, 12158477739023616000, 605960547270414336000, 32087688283562655744000 (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 617

FORMULA

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

Recurrence: {a(1)=1, a(0)=1, a(2)=8, (12+2*n^3+12*n^2+22*n)*a(n)+(-n^2-5*n-6)*a(n+1)+(-3*n-9)*a(n+2)+a(n+3)=0}

Sum(-1/229*(-5-74*_alpha+16*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(1-3*_Z-_Z^2+2*_Z^3))*n!

a(n) = n!*A052550(n). - R. J. Mathar, Nov 27 2011

MAPLE

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

CROSSREFS

Sequence in context: A188450 A121766 A052620 * A076527 A247112 A166815

Adjacent sequences:  A052666 A052667 A052668 * A052670 A052671 A052672

KEYWORD

easy,nonn

AUTHOR

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

STATUS

approved

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Last modified July 5 01:22 EDT 2020. Contains 335457 sequences. (Running on oeis4.)