[seqfan] Re: Unknowns in A281571

M. F. Hasler oeis at hasler.fr
Thu Apr 27 05:57:07 CEST 2017

> At present there is no escape clause in the definition to say what to do if
> no such k exists.  This is OK, I think, because by the usual heuristic argument
> using the prime number theorem, k *should* always exist.

I would be in favour of adding this "escape clause", because there is
not only the PNT:
unless disproved, there could be a correlation in divisibility
properties of n and concat(n,n+1,...,n+m) which makes that none of the
concatenations can be prime, for some n.

I also computed the so far unknown terms a(18) = 586, a(28) = 934,
a(35) = 947, a(51) = 1325,
and specified a (my) search limit for earlier terms which are larger
than that (if they exist).

- Maximilian

> On Wed, Apr 26, 2017 at 7:03 PM, Hans Havermann <gladhobo at bell.net> wrote:
> > https://oeis.org/A281571
> > "Sequence lists... -1 if such a number is unknown." I thought this was a
> > no-no. Doesn't an unknown stop the sequence from continuing?

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