Let’s start with the notion of primality radius of a positive integer, which I came to think of while working on Goldbach’s conjecture.

By definition, given a positive integer , the non negative integer is a primality radius of if and only if both and are prime numbers.

A prime has trivially a primality radius equal to , but the concept becomes really interesting when one considers a composite integer. For example, it is easy to check that is the smallest primality radius of .

The famous twin prime conjecture is equivalent to the following statement:

« is a primality radius of infinitely many positive integers »

whereas Goldbach’s conjecture simply becomes:

« every positive integer admits a primality radius ».

Obviously, can only be a primality radius of provided .

Here comes an almost copy-paste version of a question of mine on MathOverflow:

« Let’s define the number , which depends on $n$, in the following way:

where is the number of primes less or equal to .

is a prime only if for all prime less or equal to :

doesn’t divide .

There are exactly such primes.

The number will be called the « natural configuration order » of .

Now let’s define the « -order configuration » of an integer , denoted by , as the following sequence:

For example:

I call the « natural configuration » of .

To make a non negative integer be a primality radius of , one can require the following condition:

1) For all integer such that :

differs from

and

differs from .

If this statement 1) is true, then will be called a « potential typical primality radius » of .

Moreover, if , then will simply be called a « typical primality radius » of .

Now let’s define:

– as the number of potential typical primality radii of (hence less than but potentially greater than )

where:

– as the number of typical primality radii of $n$

– by the following equality:

It is quite easy to give an exact expression of and to show that:

, where is a positive constant.

A statistical heuristics* makes me think that: .

I wonder whether this last statement is equivalent to RH (Riemann Hypothesis) or not. If so, it would mean that RH implies that every large enough even number is the sum of two primes. »

*the statistical heuristics I refer to is:

with the « probability » of an integer less than to be a potential typical primality radius of

hence

and the « frequency » of the event « being a typical primality radius of « .

so that .

This gives:

This is, up to the implied constant, the error term in the explicit formula of under RH.

I was told several years ago by a brilliant youngster that such an upper bound for implies GRH (Generalized Riemann Hypothesis, that deals with Dirichlet L-functions). The big deal is thus to prove some kind of converse implication.