This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A007145 M3605 #26 Nov 07 2021 15:28:08
%S A007145 1,0,1,4,24,193,2420,47912,1600524,93253226,9694177479,1822463625183,
%T A007145 625829508087155,395785845695978077,464137111800208818956,
%U A007145 1015091598240432264958267,4160447480034069826186309689,32088552194861245127627790541334
%N A007145 Number of rooted bridgeless graphs with n nodes.
%D A007145 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A007145 Andrew Howroyd, <a href="/A007145/b007145.txt">Table of n, a(n) for n = 1..40</a> (terms 1..22 from R. J. Mathar, terms 21..22 corrected by Andrew Howroyd)
%H A007145 P. Hanlon and R. W. Robinson, <a href="http://dx.doi.org/10.1016/0095-8956(82)90048-X">Counting bridgeless graphs</a>, J. Combin. Theory, B 33 (1982), 276-305.
%o A007145 (PARI) \\ See A004115 for graphsSeries and A339645 for combinatorial species functions.
%o A007145 cycleIndexSeries(n)={my(g=graphsSeries(n), gcr=sPoint(g)/g); sSolve( gcr, x*sv(1)*sExp(gcr) )}
%o A007145 NumUnlabeledObjsSeq(cycleIndexSeries(15)) \\ _Andrew Howroyd_, Dec 27 2020
%Y A007145 Cf. A004115, A007146.
%K A007145 nonn,nice
%O A007145 1,4
%A A007145 _N. J. A. Sloane_
%E A007145 Reference gives first 22 terms (terms a(21) and a(22) contain typos).
%E A007145 More terms from _R. J. Mathar_, Jun 06 2007