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Old 2009-09-15, 22:12   #45
philmoore
 
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"Phil"
Sep 2002
Tracktown, U.S.A.

21378 Posts
Default New sieve file just uploaded

Well now there are 309,722 candidates left in the sieve file. We just uploaded a new one, almost 1.85% smaller, mainly due to the removal of everything with factors between 200 trillion and 350 trillion. Actually, that only accounts for 1.67% smaller, I had also forgotten to remove the candidates with factors between 180 trillion and 190 trillion in the previous file. Thanks Geoff and Kent, and a big thank you to Lennart Vogel, who took some time out of his PrimeGrid work to do a big chunk of sieving for us! The three of you have together eliminated about 1 out of every 60 remaining candidates.

The new file will not speed up the sieving significantly, but it will reduce the number of factors reported on already eliminated numbers (by about 1.85%). I think our sieving status is much better now, I would think that we should be somewhere between 400 and 500 trillion at this point, and we will be at 400T before too long. The question of optimum sieve level is tricky. Every hour of sieving effort eventually saves much more time in PRP work, but not right away. At our current sieve level, I estimate that an hour of sieving work will save an hour of PRP work on average by time the exponents get up to around 7 to 8 million or so (depending upon whether you are doing 64-bit or 32-bit sieving.) If we expect at least one of these two sequences to survive to a high value of n, we eventually should sieve much deeper. Seventeen or Bust is doing their sieving work jointly with the Prime Sierpinski Project through PrimeGrid, which has the advantage of mobilizing large numbers of computers. We might eventually go the same route, but I am comfortable with this being a small project for now. What do the rest of you think?

Also, if anyone has benchmarks for the new sieve file, I would appreciate hearing of them.

Last fiddled with by philmoore on 2009-09-15 at 22:13
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