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A052735
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A simple context-free grammar in a labeled universe.
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0
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0, 0, 2, 6, 48, 480, 6480, 105840, 2056320, 46085760, 1172102400, 33330528000, 1048055500800, 36104266598400, 1352222474803200, 54706557185280000, 2377540306132992000, 110466555918630912000, 5464214679506558976000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 691
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FORMULA
| E.g.f.: 1/2-1/2*x-1/2*(1-2*x-3*x^2)^(1/2)
Recurrence: {a(1)=0, a(2)=2, (-3*n^2+3)*a(n)+(-1-2*n)*a(n+1)+a(n+2)}
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MAPLE
| spec := [S, {C=Prod(B, S), B=Union(S, Z, C), S=Prod(B, Z)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A195203 A052743 A052587 * A052717 A175430 A129464
Adjacent sequences: A052732 A052733 A052734 * A052736 A052737 A052738
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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