[seqfan] Re: Numbers NOT of the form 2^x - y^2

[Neil Sloane]

These are deep waters - you need to read David Cox's book,
Primes of the form x^2+ny^2.

It is not enough to look at the modular restrictions (which is to say, the
genus of the form).


On Tue, Oct 7, 2014 at 10:34 AM, Charles Greathouse <
charles.greathouse at case.edu> wrote:

> Is there a number n such that A200522(n) = 0 but n is not in A051213? That
> is, are modular restrictions the only obstacle to membership?
>
> Charles Greathouse
> Analyst/Programmer
> Case Western Reserve University
>
> On Tue, Oct 7, 2014 at 1:26 AM, Frank Adams-Watters <franktaw at netscape.net
> >
> wrote:
>
> > A200522 appears to be the answer.
> >
> > Franklin T. Adams-Watters
> >
> > -----Original Message-----
> > From: Alonso Del Arte <alonso.delarte at gmail.com>
> > To: Sequence Fanatics Discussion list <seqfan at list.seqfan.eu>
> > Sent: Mon, Oct 6, 2014 11:38 pm
> > Subject: [seqfan] Numbers NOT of the form 2^x - y^2
> >
> >
> > A sequence from Juri-Stepan raises for me a question I find very
> > interesting: how can you be absolutely sure a number is NOT of the form
> 2^x
> > - y^2 ? The answer would also be relevant for the supersequence, A051213.
> >
> > Since Juri's subsequence consists of the prime numbers of the form, I had
> > the foggy notion that Legendre's symbol is relevant, but I can't figure
> out
> > if I'm on the right track with that.
> >
> >
> >
> > _______________________________________________
> >
> > Seqfan Mailing list - http://list.seqfan.eu/
> >
>
> _______________________________________________
>
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>



-- 
Dear Friends, I have now retired from AT&T. New coordinates:

Neil J. A. Sloane, President, OEIS Foundation
11 South Adelaide Avenue, Highland Park, NJ 08904, USA.
Also Visiting Scientist, Math. Dept., Rutgers University, Piscataway, NJ.
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