[A058387] Series-Parallel Confusion

[Jon Awbrey]

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Gordon Royle wrote:
> 
> I am confused about  A058387
> 
> http://www.research.att.com/cgi-bin/access.cgi/as/njas/sequences/eisA.cgi?Anum=A058387
> 
> which lists the numbers of series-parallel networks on n unlabelled edges
> with no multiple edges.
> 
> According to this there are
> 
> 0 on 0 edges
> 1 on 1 edge     (x---x)
> 1 on 2 edges    (x---x---x)
> 
> 2 on 3 edges..
> 
> But according to the definition of series-parallel
> with which I am familiar we should have 3 here --
> a path of length 3, a 3-star and a triangle.

i think it has to have 1 input node and 1 output node, so K_1,3 is out.

jon awbrey

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