Numbers Composites Lowest
3*2^n-1by nby size738 c162904 c151
5*2^n-1by nby size844 c245900 c182
7*2^n-1by nby size729 c189786 c167
9*2^n-1by nby size753 c198847 c154
11*2^n-1by nby size731 c168956 c165
13*2^n-1by nby size957 c244976 c163
15*2^n-1by nby size747 c194837 c164
All k*2^n-1by nby size  
3*2^n+1by nby size722 c179806 c139
5*2^n+1by nby size725 c185763 c146
7*2^n+1by nby size728 c158856 c148
9*2^n+1by nby size728 c182737 c158
11*2^n+1by nby size721 c193803 c151
13*2^n+1by nby size715 c159933 c142
15*2^n+1by nby size719 c181844 c145
All k*2^n+1by nby size  
All numbersby nby size  

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Latest factor

Number Input Factor Cofactor Method Arguments Who Date (CET)
13*2^985-1c264p52=9983650704281157423294596765728363484978679112057043c212ECM B1=48e7, sigma=3:3169435538M Curtis2024-07-07 19:52

50 latest factors


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 gmp-ecm 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

Links to various factoring programs can be found here.

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Factors of k*2^n-1 for k=3,5,7,9, n≤650 were previously collected by Sander Hoogendoorn and
factors of 11*2^n-1 for n≤650 by Robert Backstrom.

© Mikael Klasson (anything @ this site)
® 28 Dec 2021 11:25:51