A304070 Number of simple graphs with n vertices rooted at a pair of distinguished vertices.

0, 2, 8, 40, 240, 1992, 24416, 483040, 16343872, 982635280, 106979975168, 21285548190080, 7783083940331520, 5254164116114948480, 6577258363669088914432, 15332656940815954900371968, 66830735142688170751257497600, 546722015615195079134707942219904

Offset: 1

Author

Brendan McKay, May 05 2018

Keywords

• nonn

Comments

The graphs do not need to be connected.

Examples

			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.
		

Links

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

Crossrefs

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

Formula

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

Extensions

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