20140114, 22:50  #23 
Nov 2003
2·1,811 Posts 
Hi diep,
Yes, there is a jump in the length of the used FF transform, from about 144k to 160k, at n=2750k. The next jump to 192k will appear at n=3274k. 
20140114, 23:06  #24 
Sep 2006
The Netherlands
2×3^{2}×43 Posts 
Ah many thanks!
So the next jump makes it extra tough to find stuff of 1M digits :) After a slow start first few months, it's 16 cores now which went steady, yet i guess i soon have to increase that to 32+ cores to keep the momentum because of the huge slowdowns. Too bad i can't throw into battle the gpu's yet. Know a description of how it works with this fft len size and the used transform? I have a book from Pomerance & Crandall, yet those descriptions are not very usable to write code from and so far it seems one of the few books at least attempting to describe something :) The FFT i implemented a few years ago, it works in a power of 2 larger. So to calculate n limbs one needs an array sized 2n limbs, which simply would mean a single 8 core box is same speed like 1 GPU, instead of the GPU being roughly 5x faster (Tesla C2075's i have here) or more than a single 8 core Xeon box here :) 
20140115, 11:27  #25 
"Carlos Pinho"
Oct 2011
Milton Keynes, UK
3·1,657 Posts 
Hi diep,
I found this: 69*2^24282511 is prime! (730979 decimal digits) Time : 2077.484 sec. HEHEHEHEHEHE 
20140115, 14:06  #26 
Sep 2006
The Netherlands
2×3^{2}×43 Posts 
Congratulations!

20140115, 14:14  #27 
Sep 2006
The Netherlands
306_{16} Posts 
Did you finish it now to 2.5M?
As i started at 2.5M as appointed. It's testing to 3M here now in the current batch. Last fiddled with by diep on 20140115 at 14:15 
20140115, 14:48  #28  
"Carlos Pinho"
Oct 2011
Milton Keynes, UK
3×1,657 Posts 
Quote:
Check progress here: http://www.mersenneforum.org/showthread.php?t=14087 

20140115, 14:53  #29 
Sep 2006
The Netherlands
2·3^{2}·43 Posts 
Maybe you find another few primes there, let's hope so!
As for 69, note after this 2.41M find i hadn't expected in the range till 3M for another 2 at least to be there! I thought: "maybe there is one around 2.8Mbit". Yet already 2 showed up now :) Last fiddled with by diep on 20140115 at 14:55 
20140415, 23:23  #30 
Sep 2006
The Netherlands
2·3^{2}·43 Posts 
Last cores will take some time to finish yet 3M nearly completed.
Divided 3M4M into pieces. Cores already busy short while there. Maybe the gem shows up as the last to be checked! All machines being equipped with ECC is tough to blame on a bitflip in RAM :) If the crashed internet machine here fixed and other IT stuff might have look at CUDA again for doing Riesel with it. 
20140509, 22:30  #31 
Sep 2006
The Netherlands
1406_{8} Posts 
Prime!
69 * 2 ^ 3097340  1 is prime Please can one or more try to verify? Thanks, Vincent 
20140509, 23:25  #32 
"Carlos Pinho"
Oct 2011
Milton Keynes, UK
3·1,657 Posts 
If you trust your hardware just submit it. Only within an hour I will have an open slot to test this number.

20140509, 23:25  #33 
Sep 2002
Database er0rr
7442_{8} Posts 
Code:
69*2^30973401 is prime! Time : 2579.994 sec. 