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A052722
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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, 0, 120, 3600, 100800, 3024000, 99792000, 3632428800, 145297152000, 6351561216000, 301699157760000, 15487223431680000, 854894733428736000, 50516506975334400000, 3182539939446067200000, 212985365178313728000000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,6
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 678
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FORMULA
| E.g.f.: (-1/2+1/2*(1-4*x)^(1/2)+x)^2*(1/2-1/2*(1-4*x)^(1/2))
Recurrence: {a(1)=0, a(2)=0, a(4)=0, a(3)=0, a(5)=120, (-2*n^2+22*n+20-4*n^3)*a(n)+(19*n-14+13*n^2)*a(n+1)+(-7*n-9)*a(n+2)+a(n+3)}
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MAPLE
| spec := [S, {C=Union(B, Z), B=Prod(C, C), S=Prod(B, B, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A060490 A158048 A183266 * A139389 A166596 A000514
Adjacent sequences: A052719 A052720 A052721 * A052723 A052724 A052725
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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