# [seqfan] Re: No "-1" value in A047949?

Charles Greathouse charles.greathouse at case.edu
Sun Mar 14 00:28:21 CET 2010

```a(n) is n-2 infinitely often, and the value doesn't stray too far from
there in any case -- no further than n-173 in Noe's first 10,000.
Calculus suggests that the n - log(n)^(2 + eps) will be roughly in the
right order of magnitude for a lower bound, and n - k log(n)^3 should
be a lower bound if there isn't anything funny going on.  But I
haven't looked at it closely.

Charles Greathouse
Analyst/Programmer
Case Western Reserve University

On Sat, Mar 13, 2010 at 5:38 PM, Jonathan Post <jvospost3 at gmail.com> wrote:
> It looks to me as if no "-1" value is there in the first 10,000
> values.  Is that correct?  Is there a proof that no such value exists?
>
> A047949         a(2) = a(3) = 0; for n >= 4, a(n) = largest m such that n-m
> and n+m are both primes, or -1 if no such m exists.
>
> What is a(n) asymptotically?
>
>
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```