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

1,2

Comments

The graphs do not need to be connected.

Links

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

Formula

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

Example

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.

Crossrefs

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

Sequence in context: A055882 A002301 A319949 * A376544 A349105 A259869

Adjacent sequences: A304067 A304068 A304069 * A304071 A304072 A304073

Keyword

nonn

Author

Brendan McKay, May 05 2018

Extensions

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

Status

approved