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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
OFFSET
0,4
COMMENTS
We consider a single edge to be 2-connected, so a(1) = 1.
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
KEYWORD
nonn
AUTHOR
Gus Wiseman, Nov 27 2018
EXTENSIONS
Terms a(7) and beyond from Andrew Howroyd, Nov 29 2018
STATUS
approved