A319612 Number of regular simple graphs spanning n vertices.

1, 0, 1, 1, 7, 13, 171, 931, 45935, 1084413, 155862511, 10382960971, 6939278572095, 2203360500122299, 4186526756621772343, 3747344008241368443819, 35041787059691023579970847, 156277111373303386104606663421, 4142122641757598618318165240180095

Offset: 0

Author

Gus Wiseman, Dec 17 2018

Keywords

• nonn

Comments

A graph is regular if all vertices have the same degree. The span of a graph is the union of its edges.

Examples

			The a(4) = 7 edge-sets:
  {{1,2},{3,4}}
  {{1,3},{2,4}}
  {{1,4},{2,3}}
  {{1,2},{1,3},{2,4},{3,4}}
  {{1,2},{1,4},{2,3},{3,4}}
  {{1,3},{1,4},{2,3},{2,4}}
  {{1,2},{1,3},{1,4},{2,3},{2,4},{3,4}}
		

Crossrefs

Cf. A002829, A005176, A110100, A116539, A295193, A306017, A319189, A319190.

Formula

a(n) = A295193(n) - 1.

Extensions

a(16)-a(18) from Andrew Howroyd, Sep 02 2019