[seqfan] Re: Sequences that use '-1' to indicate 'impossible'.

Charles Greathouse charles.greathouse at case.edu
Wed Sep 23 20:47:04 CEST 2015


To be clear: are you saying that all "... or -1 if no such number exists"
sequences should havw keyword:sign, even if no such n is known? For
example, would "a(n) = the smallest prime p such that the next prime after
p is p + 2n, or -1 if no such number exists" have keyword:sign (and change
to keyword:nonn once Polignac's conjecture is proved)?

Charles Greathouse
Analyst/Programmer
Case Western Reserve University

On Wed, Sep 23, 2015 at 11:35 AM, Neil Sloane <njasloane at gmail.com> wrote:

> Many definitions say "a(n) = ... or -1 if no
> such number exists"
>
> And -1 is a negative number, so the keyword "sign" is perfectly correct.
>
> This has been our convention for at least 30 years, so we do not want to
> change it.
>
> 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 Wed, Sep 23, 2015 at 10:04 AM, Charles Greathouse <
> charles.greathouse at case.edu> wrote:
>
> > There are cases where it would be nice to have a sigil for "undefined",
> > "does not exist", "positive infinity", etc. But I think there's too much
> > code relying on the entries to be strictly numeric for this to happen.
> >
> > Charles Greathouse
> > Analyst/Programmer
> > Case Western Reserve University
> >
> > On Wed, Sep 23, 2015 at 8:12 AM, Sidney Cadot <sidney at jigsaw.nl> wrote:
> >
> > > Hi,
> > >
> > > Some sequences use '-1' to indicate that a certain entry does not
> > > exist, e.g. A154852 and A237584.
> > >
> > > Should such sequences be considered signed (kw:sign) or unsigned
> > (kw:nonn)?
> > >
> > > Wouldn't it be more appropriate to allow an explicit "null" value in
> such
> > > cases?
> > >
> > > Regards, SIdney
> > >
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