[seqfan] Q: unlabeled 2-regular digraphs
Richard J. Mathar
mathar at mpia-hd.mpg.de
Tue Mar 12 10:18:33 CET 2019
A007107 counts the labeled 2-regular digraphs with n nodes;
in A007108 we have the connected ones, in A001499 admitting loops.
Does the OEIS show somewhere the graphs without node labels, I mean the
digraphs where indegree=outdegree=2?
The natural variants of such a sequence would be:
2-regular digraphs connected, loopless
2-regular digraphs, loopless, not necessarily connected
2-regular digraphs connected, loops allowed
2-regular digraphs, loops allowed, not necessarily connected
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