1,2

The graphs do not need to be connected.

Andrew Howroyd, Table of n, a(n) for n = 1..50

a(n) = 2*A304069(n).

a(3)=8: 1 for the graph with no edge, 3 for the graph with one edge, 3 for the graph with two edges, 1 for the triangle.

Cf. A304074 (for connected graphs), A000088 (not rooted).

Sequence in context: A055882 A002301 A319949 * A259869 A321733 A000828

Adjacent sequences: A304067 A304068 A304069 * A304071 A304072 A304073

nonn

Brendan McKay, May 05 2018

Terms a(13) and beyond from Andrew Howroyd, May 06 2018

approved