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A322140 Number of labeled 2-connected multigraphs with n edges (the vertices are {1,2,...,k} for some k). 2
1, 1, 1, 2, 7, 37, 262, 2312, 24338, 296928, 4112957, 63692909, 1089526922, 20389411551, 414146189901, 9070116944468, 212983762029683, 5336570227705763, 142083405456873290, 4004953714929148655, 119128974685786590410, 3728639072095285867881 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

We consider a single edge to be 2-connected, so a(1) = 1.

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..100

Gus Wiseman, The a(5) = 37 labeled 2-connected multigraphs with 5 edges.

PROG

(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

CROSSREFS

Cf. A002218, A002905, A013922, A275307, A291841, A304118, A304887, A322110, A322117, A322118, A322137, A322138.

Sequence in context: A135164 A321087 A072597 * A125515 A135920 A001515

Adjacent sequences:  A322137 A322138 A322139 * A322141 A322142 A322143

KEYWORD

nonn

AUTHOR

Gus Wiseman, Nov 27 2018

EXTENSIONS

Terms a(7) and beyond from Andrew Howroyd, Nov 29 2018

STATUS

approved

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Last modified September 29 12:15 EDT 2020. Contains 337431 sequences. (Running on oeis4.)