Numbers  Composites  Lowest unfactored 
Smallest composite 

3*2^n1  by n  by size  738 c162  904 c151 
5*2^n1  by n  by size  844 c245  900 c182 
7*2^n1  by n  by size  729 c189  786 c167 
9*2^n1  by n  by size  753 c198  847 c154 
11*2^n1  by n  by size  731 c168  956 c165 
13*2^n1  by n  by size  957 c244  976 c163 
15*2^n1  by n  by size  747 c194  837 c164 
All k*2^n1  by n  by size  
3*2^n+1  by n  by size  722 c179  806 c139 
5*2^n+1  by n  by size  725 c185  763 c146 
7*2^n+1  by n  by size  728 c158  856 c148 
9*2^n+1  by n  by size  728 c182  737 c158 
11*2^n+1  by n  by size  721 c193  803 c151 
13*2^n+1  by n  by size  715 c159  933 c142 
15*2^n+1  by n  by size  719 c181  844 c145 
All k*2^n+1  by n  by size  
All numbers  by n  by size 
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Please consider reserving a number if you're going to do a lot of work on that particular one, and respect other people's reservations. Check the current reservations before you embark on a big factorization effort.
Number  Input  Factor  Cofactor  Method  Arguments  Who  Date (CET) 
13*2^9761  c229  p66=803024816669649842267806087775443106364960825797498108819068769837  c163  ECM  B1=13e8, sigma=3:2028344873  M Curtis  20240623 20:21 
March 29, 2009: I've done k=15 up to n=555. Most of the factors < about 33 digits have been removed from the higher numbers. Enjoy!
You're more than welcome to participate in this factorization effort. Just download doecm, enter your name, and run. Source is included and should compile if you're using another OS as well. You will need gmpecm for it to work. Both downloading of composites and submission of found factors can be automated, leaving you to just start the program. It uses only your idle cpu time so don't worry about it slowing down your computer. You're of course welcome to skip doecm altogether and just factor the numbers in any way you see fit.
All numbers have had P±1 done to at least B1=1e8. Please let me know if you plan to do any further P±1.
If you're interested you can read some further information.
Aliquot sequences may also strike your factoring fancy.
Latest version released Mar 18, 2004
doecm v1.10 win
doecm v1.10 linux
ChangeLog
README
Links to various factoring programs can be found here.
100 largest prime factors
100 largest prime factors (P+1)
100 largest prime factors (P1)
100 largest prime factors (ECM)
100 largest prime factors (QS)
100 largest prime factors (GNFS)
100 largest prime factors (SNFS)
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Factors of k*2^n1 for k=3,5,7,9, n≤650 were previously collected by Sander Hoogendoorn and
factors of 11*2^n1 for n≤650 by Robert Backstrom.
© Mikael Klasson (anything @ this site) ® 28 Dec 2021 11:25:51 