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 A052638 E.g.f. x^2*(1+x-2x^2)/(1-2x). 0
 0, 0, 2, 18, 96, 960, 11520, 161280, 2580480, 46448640, 928972800, 20437401600, 490497638400, 12752938598400, 357082280755200, 10712468422656000, 342798989524992000, 11655165643849728000, 419585963178590208000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 584 FORMULA E.g.f.: x^2*(-x+2*x^2-1)/(-1+2*x) Recurrence: {a(1)=0, a(0)=0, a(2)=2, (-2*n-2)*a(n)+a(n+1)=0, a(3)=18, a(4)=96} 1/4*2^n*n! MAPLE spec := [S, {S=Prod(Z, Z, Union(Z, Sequence(Union(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); MATHEMATICA With[{nn=20}, CoefficientList[Series[x^2 (1+x-2x^2)/(1-2x), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Feb 29 2012 *) CROSSREFS Sequence in context: A157052 A224616 A052633 * A127553 A055357 A087291 Adjacent sequences:  A052635 A052636 A052637 * A052639 A052640 A052641 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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