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 A052730 A simple context-free grammar in a labeled universe. 0
 0, 0, 0, 6, 72, 1440, 35280, 1058400, 37376640, 1520830080, 70053984000, 3603888288000, 204806714112000, 12742502111539200, 861483843034214400, 62887137880799232000, 4929809613351727104000, 413044721987184967680000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 686 FORMULA E.g.f.: RootOf(-_Z+_Z^2+_Z^3+x)-RootOf(-_Z+_Z^2+_Z^3+x)^2-x Recurrence: {a(1)=0, a(2)=0, a(3)=6, a(4)=72, (-105*n+135*n^3+30)*a(n) +(-130-107*n+29*n^2)*a(n+1) +(-99-91*n)*a(n+2) +15*a(n+3)=0. a(n) = n!*A052703(n). - R. J. Mathar, Oct 18 2013 MAPLE spec := [S, {C=Prod(B, B), B=Union(S, Z, C), S=Prod(B, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); CROSSREFS Sequence in context: A113133 A302355 A089252 * A010796 A038095 A012242 Adjacent sequences:  A052727 A052728 A052729 * A052731 A052732 A052733 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified January 25 08:59 EST 2021. Contains 340416 sequences. (Running on oeis4.)