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A052605
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Expansion of E.g.f. x*(1-x)/(1-x-x^3).
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0
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0, 1, 0, 0, 24, 120, 720, 10080, 120960, 1451520, 21772800, 359251200, 6227020800, 118313395200, 2440992153600, 53614649088000, 1255367393280000, 31300493672448000, 825906208038912000
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OFFSET
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0,5
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LINKS
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FORMULA
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E.g.f.: x*(-1+x)/(-1+x+x^3).
Recurrence: a(1)=1, a(0)=0, a(2)=0, (-11*n-6-n^3-6*n^2)*a(n) +(-n-3)*a(n+2) +a(n+3) = 0.
Sum(1/31*(_alpha+11*_alpha^2-3)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+_Z^3))*n!.
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MAPLE
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spec := [S, {S=Prod(Z, Sequence(Prod(Z, Z, Z, Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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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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