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A052724
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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, 0, 24, 240, 2160, 30240, 524160, 9434880, 188697600, 4311014400, 108254361600, 2939153817600, 86568043161600, 2753962219008000, 93838712647680000, 3409619685728256000, 131735241369059328000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,5
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 680
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FORMULA
| E.g.f.: (1/2)/x^2*(1-x-(1-2*x+x^2-4*x^3)^(1/2))-(1/2)/x*(1-x-(1-2*x+x^2-4*x^3)^(1/2))-x
Recurrence: {a(1)=0, a(2)=0, a(3)=0, a(4)=24, a(6)=2160, a(7)=30240, (38*n^4+120*n^3-48-4*n+130*n^2+4*n^5)*a(n)+(-193*n^2-52*n^3-302*n-5*n^4-168)*a(n+1)+(96+29*n^2+92*n+3*n^3)*a(n+2)+(-52-3*n^2-25*n)*a(n+3)+(n+6)*a(n+4), a(5)=240}
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MAPLE
| spec := [S, {B=Prod(Z, C), C=Union(B, S, Z), S=Prod(B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A014340 A052753 A052520 * A000536 A151720 A052652
Adjacent sequences: A052721 A052722 A052723 * A052725 A052726 A052727
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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