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 A052606 E.g.f. (1-x)^2/(1-4x+x^2). 0
 1, 2, 16, 180, 2688, 50160, 1123200, 29342880, 876072960, 29425939200, 1098191001600, 45083550758400, 2019049224192000, 97957525739673600, 5118154482618777600, 286518188551795200000, 17108806991486386176000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 551 FORMULA E.g.f.: (-1+x)^2/(1-4*x+x^2) Recurrence: {a(0)=1, a(1)=2, (n^2+3*n+2)*a(n)+(-4*n-8)*a(n+1)+a(n+2)=0, a(2)=16} Sum(-1/3*(-1+2*_alpha)*_alpha^(-1-n), _alpha=RootOf(1-4*_Z+_Z^2))*n! MAPLE spec := [S, {S=Sequence(Prod(Sequence(Z), Sequence(Z), Union(Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); CROSSREFS Sequence in context: A138014 A206988 A217360 * A011553 A291816 A123898 Adjacent sequences:  A052603 A052604 A052605 * A052607 A052608 A052609 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified June 20 23:24 EDT 2021. Contains 345312 sequences. (Running on oeis4.)