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%I #12 Dec 02 2020 17:50:34
%S 1,2,7,21,73,255,946,3618,14376,58957,249555,1087828,4878939,22488282,
%T 106432530,516783762,2572324160,13116137104,68461594211,365559412868,
%U 1995532789212,11129600885183,63381069498524,368338847181336,2183239817036378
%N Number of unlabeled connected simple graphs with n edges rooted at two indistinguishable vertices.
%F G.f.: f(x)/g(x) - (r(x)^2 + r(x^2))/2 where f(x), g(x) and r(x) are the g.f.'s of A339064, A000664 and A339039.
%o (PARI) \\ See A339063 for G.
%o 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 Cf. A000664, A002905, A303831, A303832, A339039, A339040, A339043, A339044, A339063, A339064.
%K nonn
%O 1,2
%A _Andrew Howroyd_, Nov 20 2020
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