[Question about missing terms]

[Christian G. Bower]

"Mark Hudson" <mrmarkhudson at hotmail.com> wrote:
...
> what is the correct protocol for submitting a sequence when one 
> knows many terms, say from a(1) to a(N), but does not know the values
> for some m: 1<=m<=N?
> 
> Could I submit a sequence with "?" marking the missing terms?

Marc LeBrun
> The best thing is to use some "flag" value, such as 0 or -1, outside the
> range of a(n).

I've never seen flags used to indicate unknown values, only to indicate
when no value exists. Cf. A046056 for an example.

I don't think this method is good for unknown values, as it would be
counter-intuitive to enter values into a sequence that are known to be
wrong. (Although it could work if well commented. Neil will have to make
the decision.)

What has been done in the past is to list all the known values up to the
first unknown when, and then use a comment or extension line to explain
what else is known. Cf A027623 for an example.

Christian