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 A052661 E.g.f. (2-3x)/((1-x)(1-x-x^2)). 0
 2, 1, 4, 12, 72, 480, 4320, 45360, 564480, 7983360, 127008000, 2235340800, 43110144000, 902918016000, 20399720140800, 494300911104000, 12783824621568000, 351419178958848000, 10230993181753344000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 608 FORMULA E.g.f.: -(-2+3*x)/(-1+x+x^2)/(-1+x) Recurrence: {a(1)=1, a(2)=4, a(0)=2, (n^3+6*n^2+11*n+6)*a(n)+(-2*n-6)*a(n+2)+a(n+3)=0} (1+Sum(1/5*(-1+3*_alpha)*_alpha^(-1-n), _alpha =RootOf(-1+_Z+_Z^2)))*n! a(n) = n!*A001611(n-1), n>0. - R. J. Mathar, Nov 27 2011 MAPLE spec := [S, {S=Union(Sequence(Z), Sequence(Prod(Z, Z, Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); CROSSREFS Sequence in context: A088137 A205870 A064297 * A225117 A088624 A066409 Adjacent sequences:  A052658 A052659 A052660 * A052662 A052663 A052664 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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