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A052878
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A simple grammar.
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0
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0, 2, 6, 34, 276, 2928, 38520, 606240, 11118240, 232928640, 5488922880, 143707737600, 4138613740800, 130021152307200, 4425207423436800, 162194949242726400, 6369480464675328000, 266808295408951296000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 849
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FORMULA
| E.g.f.: ln(-(-1+x)/(1-3*x+x^2))
Recurrence: {a(1)=2, a(2)=6, a(3)=34, (-n^3-2*n-3*n^2)*a(n)+(4*n^2+12*n+8)*a(n+1)+(-4*n-8)*a(n+2)+a(n+3)}
GAMMA(n + 1)*(4*RootOf(_Z^2 - 3*_Z + 1)^4 - 30*RootOf(_Z^2 - 3*_Z + 1)^3 + 4*RootOf(_Z^2 - 3*_Z + 1)^n*RootOf(_Z^2 - 3*_Z + 1)^3 - 21*RootOf(_Z^2 - 3*_Z + 1)^n*RootOf(_Z^2 - 3*_Z + 1)^2 + 4*(3 - RootOf(_Z^2 - 3*_Z + 1))^(n + 1)*RootOf(_Z^2 - 3*_Z + 1)^2 + 74*RootOf(_Z^2 - 3*_Z + 1)^2 - 15*(3 - RootOf(_Z^2 - 3*_Z + 1))^(n + 1)*RootOf(_Z^2 - 3*_Z + 1) - 63*RootOf(_Z^2 - 3*_Z + 1) + 29*RootOf(_Z^2 - 3*_Z + 1)^n*RootOf(_Z^2 - 3*_Z + 1) + 11*(3 - RootOf(_Z^2 - 3*_Z + 1))^(n + 1) - 6*RootOf(_Z^2 - 3*_Z + 1)^n + 9)/(2*RootOf(_Z^2 - 3*_Z + 1)^3 - 13*RootOf(_Z^2 - 3*_Z + 1)^2 + 27*RootOf(_Z^2 - 3*_Z + 1) - 18)/( - 1 + RootOf(_Z^2 - 3*_Z + 1))
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MAPLE
| spec := [S, {B=Sequence(Z, 1 <= card), C=Union(Z, B), S=Cycle(C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A019032 A108424 A002685 * A168362 A076863 A191742
Adjacent sequences: A052875 A052876 A052877 * A052879 A052880 A052881
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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