[seqfan] Re: Q: unlabeled 2-regular digraphs

[Brendan McKay]

I just added  A306827,
Isomorphism classes of connected 2-in 2-out digraphs, allowing parallel 
edges but not loops.

Someone might like to add the derived sequence without the connectivity 
requirement.

Brendan.

On 12/3/19 8:18 pm, Richard J. Mathar wrote:
> 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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