[seqfan] Re: Subject: Need help computing a number

[Robert Gerbicz]

"If 104916 takes m steps, the prime reached will be 104917*2^m - 1,"

>From http://www.prothsearch.com/rieselprob.html
the 104917*2^340181-1 is prime. Maybe 340181 is also the smallest exponent.

Neil Sloane <njasloane at gmail.com> ezt írta (időpont: 2024. júl. 30., K,
20:06):

> Dear Math Fun, Sequence Fans,
>
> Start with an integer k, 13 say, and repeatedly double it and add 1 until
> reaching a prime:
>
> 13 -> 27 -> 55 -> 111 -> 223.
>
> This took 4 steps, so we set R(13) = 4. This is called Riesel's problem,
> and if we never reach a prime we set R(k) = 0. The sequence R(k) is
> A050412.
> I think Riesel showed R(509203) = 0, and it seems it is believed that R(k)
> != 0 for k<509203.
>
> For another sequence (A374965) that Harvey Dale and I have been studying,
> we badly need the value of R(104916). Can someone help?  If 104916 takes m
> steps, the prime reached will be 104917*2^m - 1,
>
> so we don't actually need to see the prime (just m).
>
> I ran a naive Mathematica program (from A050412) on my iMAC, but I killed
> it after nearly 24 hours.
>
>  I have no idea how far it got.  The bottleneck is presumably the primality
> testing, but I don't know who has the fastest program for that.
> Best regards
> Neil
>
> Neil J. A. Sloane, Chairman, OEIS Foundation.
> Also Visiting Scientist, Math. Dept., Rutgers University,
> Email: njasloane at gmail.com
>
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