[seqfan] Re: minor correction of A000230

[Russell Webb]

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
> >
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> >
>
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