Quote Originally Posted by axn View Post
As a reality check: sieving from 25P to 200P will eliminate roughly 1-ln(25P)/ln(200P) = 5.2% candidates only. So as a rule of thumb, no more than 5% of resource should be spent in sieving.
While this is correct, these 5 percent of work should be done before the other 95% of work. So, now, the higher the percentage of work spent on sieving, the better. Later, sieving will be stopped, and LLR togehter with P-1 will be 100% of the work.
This begs a question that's been bugging me the last couple days - is it possible while sieving for a memory or CPU error to remove a (potentially prime) candidate in error?

Is there some sort of built in check that prevents this?
Yes; checking for this is very easy, and is done by the server once factors are submitted.
I havn't looked at P-1 lately but that may be near no longer optimal :couch:
I have. We are near the threshold of efficiency, but Prime95 still agrees to run P-1 when started with

Pfactor=k,2,17M,1,55,1.6,0

Meaning that even at a sieve depth of 2^55, it will be worth. Currently, we are at around 2^54.* . Yet, when sieving will approach 40P or 50P, we will have to reevaluate the question. Later, when firstpass reaches around 22M, P-1 will be effective even if we have sieved to 200P or 300P.

H.