(This is a follow-up to my previous questions Natural models of graphs?.)
Erdös in The Representation of a Graph by Set Intersections (1966) states:
Theorem. Let be an arbitrary
graph. Then there is a set and a
family of subsets of
which can be put into one-to-one
correspondence with the vertices of
in such a way that and are joined by an
edge of iff
and .
If we identify with a set of prime numbers and each with the product of its members we get the following:
Corollary. Let be an arbitrary finite
graph. Then there is a sequence of natural numbers
which can be put into one-to-one
correspondence with the vertices of
in such a way that and are joined by an edge iff and GCD.
We can choose the prime numbers (the elements of , from which the are built) arbitrarily, and so the question arises, whether they can always be choosen in such a way, that the set is an arithmetic sequence.
Of course every complete graph on nodes can be represented by an arithmetic sequence: just take some consecutive sequence of even numbers. Green-Tao's Theorem guarantees that also every empty graph on nodes can be represented by an arithmetic sequence of primes.
Question: Can every graph on nodes be represented by an arithmetic sequence
of natural numbers such that and are joined by an edge iff and GCD
This would be one kind of natural model of a graph, that I was looking for, originally.
Maybe some references?
Added: Due to Kevin's concise answer and Thomas' comment, I'd like to add the following question:
Question: If not every graph on nodes can be represented by an arithmetic sequence
of natural numbers such that and are joined by an edge iff and GCD: Are there interesting classes of graphs with this property?
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