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A052519
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Number of pairs of cycles of cardinality at least 3.
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0
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0, 0, 0, 0, 0, 0, 80, 840, 7896, 76608, 793152, 8838720, 106096320, 1368956160, 18928615680, 279530334720, 4394135692800, 73295141068800, 1293442388582400, 24082259707699200, 471874122729676800
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,7
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 85
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FORMULA
| E.g.f.: ln(-1/(-1+x))^2-2*ln(-1/(-1+x))*x-ln(-1/(-1+x))*x^2+x^2+x^3+1/4*x^4
Recurrence: {a(1)=0, a(2)=0, a(4)=0, a(3)=0, a(6)=80, a(5)=0, (-n^2+n^3-2*n)*a(n)+(-2*n^2+n+3)*a(n+1)+(n-1)*a(n+2)}
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MAPLE
| Pairs spec := [S, {B=Cycle(Z, 3 <= card), S=Prod(B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A062911 A024392 A200550 * A198400 A182680 A203347
Adjacent sequences: A052516 A052517 A052518 * A052520 A052521 A052522
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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