[seqfan] Re: minor correction of A000230

[Neil Sloane]

Yes, -1 is the preferred value for the escape clause

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 10:48 AM Russell Webb <nthlab at gmail.com> wrote:

> Thanks, Neil.
>
> Do you have advice on what value to use for the fall-back value?  Clearly
> should be an otherwise invalid value.  Is -1 preferred for sequences that
> are otherwise positive?
>
> Russ
>
> On Wed, Aug 18, 2021 at 9:57 AM Neil Sloane <njasloane at gmail.com> wrote:
>
> > 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
> > >
> > > --
> > > Seqfan Mailing list - http://list.seqfan.eu/
> > >
> >
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> >
>
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