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A052640
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E.g.f. x*(1-x)/(1-2*x-x^2+x^3).
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0
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0, 1, 2, 18, 144, 1680, 22320, 352800, 6330240, 128096640, 2877638400, 71131737600, 1917922406400, 56024506137600, 1762396334899200, 59401108166400000, 2135568241078272000, 81575844571533312000
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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*(-1+x)/(x^3-x^2-2*x+1)
Recurrence: {a(1)=1, a(0)=0, a(2)=2, (n^3+6*n^2+11*n+6)*a(n)+(-n^2-5*n-6)*a(n+1)+(-2*n-6)*a(n+2)+a(n+3)=0}
Sum(1/7*(-_alpha+_alpha^2+1)*_alpha^(-1-n), _alpha=RootOf(_Z^3-_Z^2-2*_Z+1))*n!
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MAPLE
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spec := [S, {S=Prod(Z, Sequence(Prod(Z, Union(Z, Sequence(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*(-1+x)/(x^3-x^2-2*x+1), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Oct 10 2023 *)
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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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