20081225, 23:12  #1 
Apr 2007
Spessart/Germany
2·3^{4} Posts 
ECM on numbers with known factors
Hello,
at the moment I want to run some Elliptic Curves on Mnumbers with known factors. Is there a possibility to tell prime95 about the already known factors? With GMPECM I simply divide out already known factors in the input file, f.e. (2^10511)/3575503 but I don't see a similary way for prime95. Thank You for every help, Matthias 
20081226, 01:02  #2 
"Nancy"
Aug 2002
Alexandria
2^{5}·7·11 Posts 
Create a file "lowm.txt" for 2^n1 numbers with content like e.g.
M( 123 )C: 456 if the number 2^1231 had the factor 456. For 2^n+1 numbers, make a file "lowp.txt" and start the line with P instead of M. If the files are in the Prime95 working directory, it scans them for known factors when it starts P1 or ECM. Alex 
20081226, 01:21  #3 
Apr 2007
Spessart/Germany
10100010_{2} Posts 
Thank you Alex, very appreciatet. I will test it immediately.
best regards (and Merry Christmas to all), Matthias 
20081226, 03:42  #4 
P90 years forever!
Aug 2002
Yeehaw, FL
2×5×23×31 Posts 
lowm.txt is no longer the preferred way of doing this.
Put in worktodo.txt: ECM2=k,b,n,c,B1,B2,curves_to_do[,specific_sigma,B2_start][,"factors"] where factors is a comma separated list of known factors 
20081226, 05:33  #5  
May 2008
1,093 Posts 
I confirm the lowm.txt file works with mprime 25.6 and earlier versions at least. I haven't used newer versions yet (is it being dropped?). Monday I found this 38 digit ECM factor:
Quote:
Good luck on your search. 

20081226, 05:57  #6  
Apr 2007
Spessart/Germany
2·3^{4} Posts 
Hello again,
Quote:
@ Jayson King I saw this factor in the 'recent cleared' list on monday, what a monster, congratulations If I remember right you already found a 41digit factor some days before (exponent range ~ 10000)... could you play lotto for me next week? best regards, Matthias 

20081226, 13:25  #7 
P90 years forever!
Aug 2002
Yeehaw, FL
1BDA_{16} Posts 
It is not being dropped. However, when ECMing k*b^n+c it only works if k=1, b=2, and c=1. The worktodo.txt approach can handle all cases.

20081226, 13:39  #8 
"Nancy"
Aug 2002
Alexandria
2^{5}×7×11 Posts 
I should add: if you use the low[mp].txt file, you can have several lines for the same input number. So when you find another factor and want to continue factoring the cofactor, you don't need to multiply the known factors up to put them in a single line  just add another line with the new factor. Plus, iirc, the exponents must be in nondecreasing order; i.e., i think Prime95 stops scanning lowm.txt for factors once it reads an exponent greater than the one it's trying to factor.
Alex 
20140424, 18:19  #9  
May 2013
Poland
3·5^{2} Posts 
Quote:
For example M118297 has known factors: 1892753, 3568547303, 404339666506801 and composite factors: 6754378613395159, 765315116799747113153, 1442905226408764139707703 and 2731063196000867551724173976359 Which to put in "factors"? 

20140424, 21:08  #10 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
21643_{8} Posts 
Just the prime factors: "1892753,3568547303,404339666506801"
Or their product  this will work too: "2731063196000867551724173976359" 
20140424, 23:10  #11  
May 2013
Poland
3·5^{2} Posts 
Quote:
ECM2=1,2,119923,1,50000,5000000,27,"1918769,8047312993,5783659875377" result "M119923 has a factor: 46542921262214092873361, AID: 9D7EF7410F11BDE1323E8C229717E099 PrimeNet success code with additional info: Composite factor 46542921262214092873361 = 8047312993 * 5783659875377 Already have factor 8047312993 for M119923 Already have factor 5783659875377 for M119923" What is wrong? 

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