A339064 - OEIS

%I #5 Nov 22 2020 12:21:54

%S 1,3,9,28,87,276,909,3086,10879,39821,151363,597062,2442044,10342904,

%T 45301072,204895366,955661003,4590214994,22675644514,115068710553,

%U 599149303234,3197694533771,17475917252052,97712883807625,558481251055893,3260409769087068

%N Number of unlabeled simple graphs with n edges rooted at two indistinguishable vertices.

%e The a(1) = 3 cases correspond to a single edge which can be attached to zero, one or both of the roots.

%o (PARI) \\ See A339063 for G.

%o seq(n)={my(A=O(x*x^n)); Vec((G(2*n, x+A, [1, 1]) + G(2*n, x+A, [2]))/2)}

%Y Cf. A000664, A053419 (one root), A303829, A339041, A339063, A339065.

%K nonn

%O 0,2

%A _Andrew Howroyd_, Nov 22 2020