[seqfan] Re: minor correction of A000230

[Neil Sloane]

1. >I take that to mean that there is no proof that such a prime exists for
all
n, and the sequence might contain -1.  However, the sequence has the "nonn"
keyword.

That is fine, don't worry about it

2. >On a related note, is it advisable to have a fall back clause for
sequences
that are not proved to exist for some n?  YES, DEFINITELY.    Or should
they be marked as such
with something like "posfin", possibly finite, or "posundef" possibly
undefined (I don't see a suitable keyword).  NO

Best regards
Neil

Neil J. A. Sloane, Chairman, 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 Wed, Aug 18, 2021 at 9:16 AM Russell Webb <nthlab at gmail.com> wrote:

> https://oeis.org/A000230
> For A000230, the description is "a(0)=2; for n>=1, a(n) = smallest prime p
> such that there is a gap of exactly 2n between p and next prime, or -1 if
> no such prime exists."
>
> I take that to mean that there is no proof that such a prime exists for all
> n, and the sequence might contain -1.  However, the sequence has the "nonn"
> keyword.
>
> Possible corrections:
> a. such a p can be proven to exist, so the "or -1 if no such prime exists"
> can be removed.  Likely true but possibly hard to prove.
> b. change to "or 0 if no such prime exists"
> c. remove the "nonn" keyword
>
> On a related note, is it advisable to have a fall back clause for sequences
> that are not proven to exist for some n?  Or should they be marked as such
> with something like "posfin", possibly finite, or "posundef" possibly
> undefined (I don't see a suitable keyword).
>
> Cheers,
> Russ
>
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