Sequences of Graphs...

Brendan McKay bdm at
Thu Dec 5 08:15:45 CET 2002

* Gordon Royle <gordon at> [021205 17:59]:
> I seek opinons on the following question:
> Some sequences of graphs on n vertices are listed in the OEIS as starting 
> from "n=0" and some from "n=1" and some (such as A054581) simply get it 
> wrong - they claim to start from n=0, but actually start from n=1.
> There is also some inconsistency.. for example, labelled trees start from 
> n=1, but unlabelled trees start from n=0.
> In general, I am not sure that anything is gained by starting *any* graph
> sequence from n=0 - it is often ambiguous or arbitrary to determine
> whether or not the null graph has a certain property, because 
> otherwise equivalent definitions often break down when n=0.

I agree, and I think that starting all graph sequences at n=1 is
the most appropriate solution.  Whether or not the null graph
actually exists, discussion of its properties is pointless.

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