20170105, 03:16  #1 
Jan 2017
3_{8} Posts 
any suitable sieve written in C or Python?
It is well known that if q  2^p  1, then q = 2px + 1 and q = 8r +() 1.
when I do some research on Fp (Fibonacci prime), I guess : 1: if q  Fp, then q = 2px + (1)^x 2: F(2n+1) must have a prime factor q, q = 2(2n+1)x + (1)^x 3: ... At this moment , I try to factor C261 ( F1565 = F5* F313 * C261), which has 261 digital. If guess is right, then C261 must have a prime factor = 2*1565*x + (1)^x. The GIMPS factoring code creates a modified sieve of Eratosthenes with each bit representing a potential 2kp+1 factor. The sieve then eliminates any potential factors that are divisible by prime numbers below 40,000 or so. Also, bits representing potential factors of 3 or 5 mod 8 are cleared. This process eliminates roughly 95% of potential factors. Since I don't know assemble language, I could not understand such code. I tried to code it by myself, but the code efficiency is very low. I have no other good choice but ask for help : Could someone provide a efficient sieve ? Thanks a lot! 
20170105, 04:34  #3 
Jun 2003
4845_{10} Posts 
Trial factoring is the wrong tool for numbers this size. You should use ECM.
Last fiddled with by axn on 20170105 at 04:35 Reason: speeling 
20170105, 04:49  #5 
Jan 2017
3 Posts 
Thanks for your advice.

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