View Single Post 2015-10-15, 12:51 #6 alpertron   Aug 2002 Buenos Aires, Argentina 31×43 Posts Well, in July I found the prime factor 782521855299947974696932851410613860657 of M1864739. I've been running the P-1 algorithm on Mersenne numbers with known factors for numbers less than M2000000. The idea is to try to find a "probably completely factored" Mersenne number, where that term means a product of primes and a probable prime. I had several successes so far: Code: (2^1790743-1)/(146840927*158358984977*3835546416767873*20752172271489035681) = PRP539014 (2^750151-1)/(429934042631*7590093831289*397764574647511*8361437834787151*17383638888678527263) = PRP225744 (2^675977-1)/(1686378749257*7171117283326998925471) = PRP203456 (2^576551-1)/4612409/64758208321/242584327930759 = PRP173528 (2^488441-1)/(61543567*30051203516986199) = PRP147012 (2^440399-1)/(16210820281161978209*31518475633*880799) = PRP132538 (2^270059-1)/540119/6481417/7124976157756725967 = PRP81265 The number at the right of "PRP" is the number of digits of that probable prime.  