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A052883
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A simple grammar.
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0
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0, 0, 2, 18, 166, 1740, 20948, 287784, 4466712, 77539680, 1491571872, 31532466240, 727281881280, 18184495230720, 490130371249920, 14170353892047360, 437524311352665600, 14370793956158976000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 856
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FORMULA
| E.g.f.: ln((-1+x)/(-1+2*x))^2
Recurrence: {a(1)=0, a(0)=0, a(2)=2, (8*n+20*n^2+16*n^3+4*n^4)*a(n)+(-36-78*n-12*n^3-54*n^2)*a(n+1)+(52+13*n^2+52*n)*a(n+2)+(-6*n-15)*a(n+3)+a(n+4), a(3)=18}
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MAPLE
| spec := [S, {B=Cycle(C), C=Sequence(Z, 1 <= card), S=Prod(B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A037728 A037623 A052865 * A052665 A092473 A073558
Adjacent sequences: A052880 A052881 A052882 * A052884 A052885 A052886
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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