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 A052656 E.g.f. x*(1+2x-4x^2)/(1-2x). 0
 0, 1, 8, 24, 192, 1920, 23040, 322560, 5160960, 92897280, 1857945600, 40874803200, 980995276800, 25505877196800, 714164561510400, 21424936845312000, 685597979049984000, 23310331287699456000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 603 FORMULA E.g.f.: x*(-2*x+4*x^2-1)/(-1+2*x) Recurrence: {a(1)=1, a(0)=0, (-2*n-2)*a(n)+a(n+1)=0, a(2)=8, a(3)=24} 2^(n-1)*n!, n>2. MAPLE spec := [S, {S=Prod(Z, Union(Z, Z, Sequence(Union(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); CROSSREFS Sequence in context: A061027 A226962 A221784 * A094061 A182589 A002268 Adjacent sequences:  A052653 A052654 A052655 * A052657 A052658 A052659 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified February 16 20:45 EST 2019. Contains 320189 sequences. (Running on oeis4.)