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

[Neil Sloane]

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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> >
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