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A201883
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The number of simple labeled graphs on n nodes such that i) all connected components have exactly one cycle, ii) all vertices have degree at most 3, iii) vertices of degree 3 are on a cycle.
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0
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1, 0, 0, 1, 15, 192, 2530, 36165, 570507, 9969400, 192525084, 4087525095, 94813475185, 2387594185944, 64886220442290, 1892895183489583, 58997625514583385, 1956486468000839280, 68781080882461076488, 2555098360335768584385, 100009432504671913008351
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OFFSET
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0,5
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LINKS
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FORMULA
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E.g.f.: ((1-x)/(1-2x))^(1/2)*exp((x^2-2x)/(4(1-x)^2)).
Let y(0)=1, y(1)=0, y(2)=0, y(3)=1/6,
Let 4ny(n)-(14n+15)y(n+1)+(18n+36)y(n+2)-(10n+30)y(n+3)+(2n+8)y(n+4)=0,
a(n) = n!*y(n).
(End)
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MATHEMATICA
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a = x/(1 - x); Range[0, 20]! CoefficientList[Series[Exp[Log[1/(1 - a)]/2 - a/2 - a^2/4], {x, 0, 20}], x]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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