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A052731
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A simple context-free grammar in a labeled universe.
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0
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0, 0, 0, 6, 48, 600, 8640, 151200, 3064320, 71124480, 1857945600, 54007430400, 1729195776000, 60483053030400, 2294881337548800, 93889711948032000, 4120492394962944000, 193100926276177920000, 9624765220305371136000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 687
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FORMULA
| E.g.f.: (1/2)/x*(1-x-(1-2*x-3*x^2)^(1/2))-1/2-1/2*x+1/2*(1-2*x-3*x^2)^(1/2)
Recurrence: {a(1)=0, a(2)=0, a(3)=6, (-15*n+15*n^3+15*n^2+3*n^4-18)*a(n)+(-n^3-7*n^2-16*n-12)*a(n+1)+(-3*n^2-16*n-21)*a(n+2)+(n+4)*a(n+3), a(4)=48, a(5)=600}
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MAPLE
| spec := [S, {C=Prod(B, Z), S=Prod(B, C), B=Union(S, Z, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A052567 A002170 A153467 * A052711 A113388 A113393
Adjacent sequences: A052728 A052729 A052730 * A052732 A052733 A052734
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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