20100802, 03:29  #1 
Oct 2007
Manchester, UK
2474_{8} Posts 
Trial Factor Bit Depth
I am sure this must have been discussed before with regards to OBD, but I could not find it.
I have just made a post in which I extended the table of trial factor depths found on The Math page of mersenne.org all the way up to billion digit numbers. Here's the post: http://www.mersenneforum.org/showpos...1&postcount=70 I have included the methodology used to attain the numbers and I would appreciate any comments on it's validity. If the numbers do turn out to be correct, then it looks like the OBD candidates need to be trial factored all the way to 87 bits, and currently there are 10 (soon to be 13) exponents at 81 bits. In terms of levels, that's high enough to take the project to level 21.01, which at the minimum would require 22 candidates at 87 bits. 
20100802, 09:57  #2 
Banned
"Luigi"
Aug 2002
Team Italia
1001011000000_{2} Posts 
87 bits on one OBD exponent would require at least 4 months of 24/7 activity on a GXT275. I guess it's premature to reach that bitdepth with actual methods...
By the time GIMPS extends 6 times its bounds, I think we'd better check fornew factors than for bitdepth. Luigi Last fiddled with by ET_ on 20100802 at 10:00 
20100802, 13:17  #3 
Aug 2006
2^{2}·1,493 Posts 

20100802, 15:05  #4  
Oct 2007
Manchester, UK
2^{2}×5×67 Posts 
Quote:
Even so, it's good to know what the ultimate goal is. 87 seems tantalizingly close as the project has several candidates at 81 bits now. We all know of course that 87 bits requires another 63 times the work to reach, but that's not as much of a carrot as saying, "JUST 6 MORE!" What do you mean by this? 

20100802, 15:26  #5  
Banned
"Luigi"
Aug 2002
Team Italia
1001011000000_{2} Posts 
Quote:
But I don't recommend following my example! The problem here is that, even using MORE_CLASSES, each class from 86 to 87 bits would last more than 3,5 hours, and interrupting the search to use the (otherwise unusable) computer would waste approximately 2 hours of calculations. Quote:
In 4 months' work we could bring 63 exponents to 80/81 bits... Luigi 

20100802, 15:52  #6  
A Sunny Moo
Aug 2007
USA (GMT5)
3×2,083 Posts 
Quote:


20100802, 16:27  #7  
Banned
"Luigi"
Aug 2002
Team Italia
2^{6}·3·5^{2} Posts 
Quote:
Luigi 

20100802, 16:34  #8 
Oct 2007
Manchester, UK
2^{2}×5×67 Posts 

20100802, 18:49  #9 
Aug 2006
2^{2}×1,493 Posts 

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