[seqfan] Re: A269254

Neil Sloane njasloane at gmail.com
Sat Oct 21 04:55:46 CEST 2017


Shouldn't there be some remarks in A269254 giving the proofs that the -1
entries do indeed correspond to sequences of non-primes?

For example, it is stated that a(7) = -1, and this is true because n=7
gives the sequence A033890, Fibonacci(4n+2), which is easily shown to be
never a prime.

But what about the other -1 entries?

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, Oct 20, 2017 at 9:58 PM, Hans Havermann <gladhobo at bell.net> wrote:

> https://oeis.org/A269254
>
> I was using a Mathematica-ized version of the MAGMA program to try to
> extend this sequence when I came across a roadblock of sorts. The MAGMA
> program suggests that if n+2 is a square then a(n) is -1. I initially
> thought that this was the only condition but my inability (so far) to
> determine a(110) has me asking if there might be other such conditions
> where the sequence is -1. More specifically, could a(110) be -1?
>
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> Seqfan Mailing list - http://list.seqfan.eu/
>


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