login
A339064
Number of unlabeled simple graphs with n edges rooted at two indistinguishable vertices.
4
1, 3, 9, 28, 87, 276, 909, 3086, 10879, 39821, 151363, 597062, 2442044, 10342904, 45301072, 204895366, 955661003, 4590214994, 22675644514, 115068710553, 599149303234, 3197694533771, 17475917252052, 97712883807625, 558481251055893, 3260409769087068
OFFSET
0,2
EXAMPLE
The a(1) = 3 cases correspond to a single edge which can be attached to zero, one or both of the roots.
PROG
(PARI) \\ See A339063 for G.
seq(n)={my(A=O(x*x^n)); Vec((G(2*n, x+A, [1, 1]) + G(2*n, x+A, [2]))/2)}
CROSSREFS
Sequence in context: A085839 A115239 A134915 * A118365 A095716 A124820
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Nov 22 2020
STATUS
approved