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A306892
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Isomorphism classes of connected 2-regular digraphs on n nodes, allowing multiarcs and loops.
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4
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OFFSET
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0,3
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COMMENTS
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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).
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LINKS
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EXAMPLE
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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.
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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