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A322140
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Number of labeled 2-connected multigraphs with n edges (the vertices are {1,2,...,k} for some k).
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2
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1, 1, 1, 2, 7, 37, 262, 2312, 24338, 296928, 4112957, 63692909, 1089526922, 20389411551, 414146189901, 9070116944468, 212983762029683, 5336570227705763, 142083405456873290, 4004953714929148655, 119128974685786590410, 3728639072095285867881
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OFFSET
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0,4
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COMMENTS
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We consider a single edge to be 2-connected, so a(1) = 1.
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LINKS
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PROG
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(PARI) seq(n)={Vec(1 + vecsum(Vec(serlaplace(log(x/serreverse(x*deriv(log(sum(k=0, n, 1/(1 - y + O(y*y^n))^binomial(k, 2) * x^k / k!) + O(x*x^n)))))))))} \\ Andrew Howroyd, Nov 29 2018
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CROSSREFS
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Cf. A002218, A002905, A013922, A275307, A291841, A304118, A304887, A322110, A322117, A322118, A322137, A322138.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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