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A052876
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Expansion of e.g.f. (exp(x)-1)^2/(-2+exp(x))^2.
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1
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0, 0, 2, 18, 158, 1530, 16622, 201978, 2724878, 40492890, 657944942, 11611834938, 221291822798, 4530383962650, 99179581033262, 2312402554523898, 57211901491595918, 1497211181084718810
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OFFSET
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0,3
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COMMENTS
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Previous name was: A simple grammar.
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LINKS
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FORMULA
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E.g.f.: (exp(x)-1)^2/(-2+exp(x))^2.
From Mario Catalani (mario.catalani(AT)unito.it), Dec 22 2003: (Start)
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MAPLE
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spec := [S, {B=Set(Z, 1 <= card), C=Sequence(B, 1 <= card), S=Prod(C, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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MATHEMATICA
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With[{nn=20}, CoefficientList[Series[((Exp[x]-1)^2/(Exp[x]-2)^2), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Jul 19 2018 *)
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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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