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

[Sidney Cadot]

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