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A052638
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E.g.f. x^2*(1+x-2x^2)/(1-2x).
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0
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0, 0, 2, 18, 96, 960, 11520, 161280, 2580480, 46448640, 928972800, 20437401600, 490497638400, 12752938598400, 357082280755200, 10712468422656000, 342798989524992000, 11655165643849728000, 419585963178590208000
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OFFSET
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0,3
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LINKS
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FORMULA
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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!
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MAPLE
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spec := [S, {S=Prod(Z, Z, Union(Z, Sequence(Union(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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MATHEMATICA
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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 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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STATUS
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approved
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