Riesel Primes k*2^n-1, k<300 [Was "k=1"]

[Cruelty]

k=25 tested till n=700000.
I'm still working on it

[VBCurtis]

Reserving k=197 and k=201. We'll test from 250k to 500k.
k=127 is complete to 575k, sieved to n=1 million (p=800B).
k=99 is complete to 260k, sieve at 1.9 trillion and counting.
k=103 is sieved to 875B (up to n=500k), starting LLR now.
-Curtis

[lsoule]

End of the month status update:
K current N
39 580k
69 735k
195 572k
231 858k

Also, I'd like to reserve k=223 again and take it a little further past n=1M

[Kosmaj]

We are about to start sieving the following 20 K's:
203, 205, 209, 211, 215, 217, 241, 245, 257, 259, 263, 265, 271, 275, 281, 283, 287, 293, 295, and 299
for the 4th Drive. We'll sieve in the n=100-600k range so that people who wish so can fill the holes on Keller's list. According to our stats and Prime Search's page (currently their web page is not on-line) all above K's have been checked to 230k, some to 250 and 260k and we'll concentrate our LLR efforts from respectively achieved limits.

The only prime found beyond the reported limit is 245*2^238468-1 found by L118 in November 2005 (k=245 reportedly checked to 230k).

Individual prime hunters for k*2^n-1, k<300 are directed to k's divisible by 3, k's less than 100 (specially for large exponents), and other available k's.

I was thinking to also include k=91, 109, 139 and 173 but I didn't because k=91 has been tested to 300k, k=109 to 350k, and k=139 to 400k while k=173 is apperently beind tested by L99. The first 3 are available for individual prime hunters too.

Please let me know if anybody has any objections/proposals regarding these 20 k's.

[MooooMoo]

Update:

k=19 has been searched to n=660,000. Other than the prime reported in the "primes found" thread two weeks ago (for n=645,555), there are no other primes in this range.

I'll continue with this k, and the residues are attached below.

[Templus]

k=93 has been completed until n=400k, still in progress

[edorajh]

Originally Posted by Kosmaj

Prime Search's page (currently their web page is not on-line)

They changed their link to:
http://www.myjavaserver.com/~primesearch/

[kar_bon]

i've reserved k=209 on prime search up to n=420.000.
current n is 382.000 and no prime found yet.

[Thomas11]

k=155 has reached n=900k. But no primes found since n=500k.
I'm continuing to n=1M...

[Kosmaj]

Thanks to everybody who replied. We have removed k=209 from our list, leaving it to Karsten. We added k=91 and k=109, so there are going to be 21 K's this time. Sieving is already under way. Our stats page is updated but the 21 K's are not marked yet.

[R. Gerbicz]

Hi all!

Are you using newpgen for sieving? Because it doesn't observe algebraic factors, as I can see! So if k is a power of a number: k=a^d ( here a>1 and d>1 ) and n is divisible by d so n=s*d, then k*2^n-1 is composite, because it is divisible by a*2^s-1.

In some cases it is a real improvement, but not very much, because in these cases you have got a very high chance that k*2^n-1 has got a "small" prime divisor, so newpgen will find it very quickly.

Note that for some k, this is a zero improvement, for example if k=49 then 49*2^(2*s)-1 is divisible by 3, so all algebraic numbers are eliminated. For k=125=5^3 all 125*2^(5*s)-1 are divisible by 31.

As I can see: up to 300 the suitable ( odd ) k values for real improvement: k=9, k=27, k=81, k=225, k=243