[seqfan] Re: defn of A167415
Neil Sloane
njasloane at gmail.com
Sat Jun 15 10:16:06 CEST 2019
Perhaps RJM could replace the existing definition of A167415 with Don
Reble's.
IIRC, Don isn't registered as an OEIS user (which is something I regret).
Best regards
Neil
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.
Phone: 732 828 6098; home page: http://NeilSloane.com
Email: njasloane at gmail.com
On Fri, Jun 14, 2019 at 9:13 PM Don Reble via SeqFan <seqfan at list.seqfan.eu>
wrote:
>
> > How is A167415 defined?
>
> It looks like,
> M such that (for all x,y except x=y=0) (x+y)^2+3xy isn't == 0 mod M.
> At any rate, this Python jot produces the sequence data.
>
> #!/usr/bin/python3
> for mod in range(2,300):
> halfmod = (mod // 2) + 1
> for x in range(halfmod):
> xsq = x * x
> for y in range(max(x,1),halfmod):
> sumsq = y * y + xsq
> xy3 = x * y * 3
> val = (sumsq + xy3) % mod
> if val == 0: break
> val = (sumsq - xy3) % mod
> if val == 0: break
> if val == 0: break
> if val != 0: print(mod)
>
>
> > %C Prime numbers of this sequence are congruent to {2,3} modulo 5.
>
> BTW, that formula equals (x^2 + 5xy + y^2);
> that may be why modulo 5 matters.
>
> --
> Don Reble djr at nk.ca
>
>
> --
> Seqfan Mailing list - http://list.seqfan.eu/
>
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