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A052742
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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, 12, 144, 2640, 64800, 1985760, 72817920, 3105527040, 150907276800, 8226772646400, 497068582348800, 32962398345676800, 2379770152465305600, 185792734381782528000, 15595576381312671744000
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,3
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LINKS
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Table of n, a(n) for n=0..16.
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 698
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FORMULA
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E.g.f.: (1/2-1/2*x-1/2*(1-6*x+x^2)^(1/2))*x
Recurrence: {a(1)=0, a(2)=2, a(3)=12, (-4*n+n^2-4+n^3)*a(n)+(-6*n^2+6-9*n)*a(n+1)+(n+1)*a(n+2)}
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MAPLE
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spec := [S, {B=Prod(C, C), C=Union(B, S, Z), S=Prod(Z, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A208866 A067601 A052740 * A035049 A010790 A221101
Adjacent sequences: A052739 A052740 A052741 * A052743 A052744 A052745
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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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