[seqfan] Giving a mathematical definition to A280001

[Natan Consigli]

Dear Seqfans,

I am trying to define A280001 mathematically with graph theory. To let
the sequence be less "obscure" I have to define what does chemical
aromaticity mean.

Here is what I did so far.

As far as being a hydrocarbon I am looking for a connected multigraph
(non looped for some authors) where each node has degree less than
five (octet rule).

For the condition of being aromatic I need a connected subset of nodes
that satisfies Huckel's rule. This means that such subset must have
the following:

1) an alternating connection 1-edge/2-edge vertices (conjugated pi system);

2) the number of 2-edge connections must be odd (4n+2 pi electrons);

3) the subset of nodes must represent a chemically planar portion of
the molecule.

I find stating rule 3 in a mathematical way very hard to do. If
anybody has ideas I would appreciate your help.

Natan Consigli