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 A339043 #14 Feb 26 2023 14:39:24
%S A339043 1,3,11,43,178,767,3425,15783,74775,363639,1811808,9239430,48175945,
%T A339043 256658465,1396152633,7750325528,43882706171,253308596926,
%U A339043 1490040961732,8928063141435,54469529215562,338236254603888,2136952452531537,13731571816349732,89710429044324926
%N A339043 Number of unlabeled connected loopless multigraphs with n edges rooted at two indistinguishable vertices.
%F A339043 G.f: f(g) - (g(x)^2 + g(x^2))/2 where x*f(x) is the g.f. of A339038 and g(x) is the g.f. of A339036.
%t A339043 seq[n_] := Module[{g, gr}, g = G[2n, x+O[x]^n, {}]; gr = G[2n, x+O[x]^n, {1}]/g; G[2n, x+O[x]^n, {1, 1}]/g - gr^2 + G[2n, x+O[x]^n, {2}]/g - (Normal[gr] /. x -> x^2) // CoefficientList[#/2, x]& // Rest];
%t A339043 seq[15] (* _Jean-François Alcover_, Dec 02 2020, after _Andrew Howroyd_'s code for G in A339065 *)
%o A339043 (PARI) \\ See A339065 for G.
%o A339043 seq(n)={my(A=O(x*x^n), g=G(2*n, x+A, []), gr=G(2*n, x+A, [1])/g); Vec(G(2*n, x+A, [1, 1])/g - gr^2 + G(2*n, x+A, [2])/g - subst(gr, x, x^2))/2}
%Y A339043 Cf. A050535, A076864, A339036, A339037, A339038, A339041, A339042, A339065.
%K A339043 nonn
%O A339043 1,2
%A A339043 _Andrew Howroyd_, Nov 20 2020