A303829 Birooted graphs: number of unlabeled graphs with n nodes rooted at 2 indistinguishable roots.

0, 2, 6, 28, 148, 1144, 13128, 250240, 8295664, 494367376, 53628829952, 10655018252544, 3893626388008448, 2627758027841688960, 3289042848785452985600, 7666804477507744021487616, 33416397343695235205887366144, 273365202164844511328577434284160

Offset: 1

Author

Brendan McKay, May 01 2018

Keywords

• nonn

Crossrefs

Cf. A303831 (connected), A303833 (trees), A126122.

Formula

a(n) = 2 * A126122(n). - Alois P. Heinz, May 01 2018