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A052599
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Expansion of e.g.f.: 1/(1-2x-x^3).
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0
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1, 2, 8, 54, 480, 5280, 69840, 1078560, 19031040, 377758080, 8331724800, 202138675200, 5349968870400, 153396430387200, 4736570917478400, 156702542540544000, 5529893367398400000, 207341583834857472000
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OFFSET
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0,2
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LINKS
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FORMULA
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E.g.f.: -1/(-1+2*x+x^3)
Recurrence: {a(0)=1, a(1)=2, a(2)=8, (-11*n-6-n^3-6*n^2)*a(n) +(-2*n-6)*a(n+2) +a(n+3)=0}
Sum(1/59*(16+12*_alpha^2+9*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^3))*n!
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Z, Prod(Z, 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[1/(1-2x-x^3), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Apr 10 2022 *)
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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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EXTENSIONS
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STATUS
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approved
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