A306892 Isomorphism classes of connected 2-regular digraphs on n nodes, allowing multiarcs and loops.

1, 1, 2, 5, 14, 50, 265, 1601, 11984, 101884

Offset: 0

Author

R. J. Mathar, Mar 15 2019

Keywords

• nonn
• more

Comments

The graphs are directed, connected and have indegree=outdegree=2 at each node. Multiarcs (connecting two nodes with the same sense of heading) and loops (edges connecting a node to itself) are permitted.

The sequence of the same family of graphs which are not necessarily connected is A006372 (the Euler transform of this sequence).

Examples

			On n=1 node, the graph is the node with two edges looping back to the node.
On n=2 nodes, the graph is either having two pairs of edges (4 edges in total) linking one node to the other, or a loop at each node and two edges (different senses) from one node to the other.
		

Links

• R. J. Mathar, OEIS A306892
• R. J. Mathar, 2-regular digraphs of the Lovelock Lagrangian, arXiv:1903.12477 [math.GM] (2019).

Crossrefs

Cf. A306827 (no loops).

Extensions

a(8) added by R. J. Mathar, Apr 08 2019

a(9) added by R. J. Mathar, Apr 15 2019