[seqfan] Re: when is 1234...n a prime?

[eli Mcfly]

Has anyone taken care to remove numbers that end in 2,4,5,6,8,and 9 from
the testing algorithm? Some code could speed up the search.
Numbers that end in 9 are removed because 123456789*100000001000000001...
Will always end in nine.
Elias Jaffe
Just a brief update -- there are no primes among first 77,000 terms.

Regards,
Max


On Tue, Sep 29, 2015 at 9:18 PM, Neil Sloane <njasloane at gmail.com> wrote:
> To Seq Fans:
>
> Consider the sequence with nth term equal to the
> concatenation of the decimal numbers 1234...n (https://oeis.org/A007908).
> When is the first prime? The comments in A007908 say
> that there should be infinitely many primes, and that there
> are no primes among the first 64000 terms.
> If you would like to help with this search, you could leave a comment
> in A007908 saying that there are no primes among terms X through Y,
> or, of course, that n = Z gives a (probable) prime, which would be
> pretty exciting.
>
>
> 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
>
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>
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