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A306892 Isomorphism classes of connected 2-regular digraphs on n nodes, allowing multiarcs and loops. 4
1, 1, 2, 5, 14, 50, 265, 1601, 11984, 101884 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
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).
LINKS
R. J. Mathar, OEIS A306892
R. J. Mathar, 2-regular digraphs of the Lovelock Lagrangian, arXiv:1903.12477 [math.GM] (2019).
EXAMPLE
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.
CROSSREFS
Cf. A306827 (no loops).
Sequence in context: A298361 A000109 A049338 * A115275 A000679 A266932
KEYWORD
nonn,more
AUTHOR
R. J. Mathar, Mar 15 2019
EXTENSIONS
a(8) added by R. J. Mathar, Apr 08 2019
a(9) added by R. J. Mathar, Apr 15 2019
STATUS
approved

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Last modified March 29 06:57 EDT 2024. Contains 371265 sequences. (Running on oeis4.)