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 A052611 E.g.f. 1/(1-2x-2x^2). 1
 1, 2, 12, 96, 1056, 14400, 236160, 4515840, 98703360, 2426941440, 66305433600, 1992646656000, 65328154214400, 2320237766246400, 88746105588940800, 3636883029491712000, 158978387626426368000, 7383729547341987840000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 556 FORMULA E.g.f.: -1/(-1+2*x+2*x^2) Recurrence: {a(0)=1, a(1)=2, (-2*n^2-6*n-4)*a(n)+(-4-2*n)*a(n+1)+a(n+2)=0} Sum(1/6*(1+2*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+2*_Z^2))*n! a(n) = n!*A002605(n+1). - R. J. Mathar, Nov 27 2011 MAPLE spec := [S, {S=Sequence(Union(Z, Z, Prod(Z, Union(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); MATHEMATICA With[{nn=20}, CoefficientList[Series[1/(1-2x-2x^2), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Apr 14 2015 *) CROSSREFS Equals 2^n * A080599(n). Sequence in context: A193425 A206855 A219119 * A340938 A059864 A095338 Adjacent sequences:  A052608 A052609 A052610 * A052612 A052613 A052614 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified June 18 04:41 EDT 2021. Contains 345098 sequences. (Running on oeis4.)