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A052743
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A simple context-free grammar in a labeled universe.
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0
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0, 1, 2, 6, 48, 480, 5040, 65520, 1048320, 18869760, 377395200, 8462361600, 209802700800, 5666588928000, 165900288153600, 5242466541312000, 177718177308672000, 6430828699975680000, 247490157968621568000
(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 699
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FORMULA
| E.g.f.: (1/2)/x^2*(1-x-(1-2*x+x^2-4*x^3)^(1/2))
Recurrence: {a(1)=1, a(3)=6, a(2)=2, a(4)=48, (-56*n^2-26*n^3-12-46*n-4*n^4)*a(n)+(n^3+7*n^2+16*n+12)*a(n+1)+(-13*n-2*n^2-21)*a(n+2)+(n+5)*a(n+3)}
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MAPLE
| spec := [S, {B=Prod(C, C), S=Union(B, Z, C), C=Prod(S, Z)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A052586 A052554 A195203 * A052587 A052735 A052717
Adjacent sequences: A052740 A052741 A052742 * A052744 A052745 A052746
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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