20160611, 17:44  #1 
Sep 2003
2583_{10} Posts 
Small inconsistencies between mersenne.org and mersenne.ca factor databases
Yesterday I noticed that Mersenne.ca had two known factors for M100003 but Mersenne.org had only one. I discovered that by sheer accident, and only because 100003 is very close to a round number.
I manually reported the "new" factor at Mersenne.org, and it gave me 0.0023 GHzdays credit. Mersenne.ca reports that this factor was originally discovered 20141206. It's not clear by whom. I decided to check all the factors below 1M. I found the following differences: * Very small fullyfactored exponents < 1000, where Mersenne.ca sometimes lists the largest factors but Mersenne.org systematically omits them. For instance M11 = 23 * 89, and Mersenne.org omits the "89". The largest of these exponents is M809. This is not really an issue, it is just mentioned for completeness. * M100003, already mentioned above * M499211, where Mersenne.ca gives a sixth factor which is actually composite, it is the product of the first, second, fourth and fifth factors (C61 = P6 * P9 * P22 * P25) * M954257, where Mersenne.ca had four known factors but Mersenne.org had only three. I manually reported the "new" factor at Mersenne.org and got 0.0283 GHzdays credit. Mersenne.ca reports this factor was originally discovered 20150602. It's not clear by whom. Some remarks: * For manuallyreported new factors of unknown origin, Mersenne.org assumes they were found by ECM at a very early stage, so very little credit was given and this didn't distort the stats. * It would be good to figure out how the inconsistency arose. Maybe look at the log files for Mersenne.org to see if the "new" factors were originally reported at the time and somehow rejected, or perhaps never reported there, or perhaps were accidentally dropped from the database somehow. As far as I know, Mersenne.ca doesn't even allow reporting of factors under 1000M, they are supposed to be reported directly to Mersenne.org instead. Or maybe it was nonGIMPS participants who originally found those factors. * It might be a good idea to systematically compare the two databases to look for more inconsistencies. However it's hard to harvest factor data from Mersenne.ca, except through very clumsy and slow screenscraping. Perhaps a compressed text file could be made available for public download, or both sites could exchange data dumps. "Browse by range" doesn't work well, for example the range http://www.mersenne.ca/exponent/browse/100001/109999 gets truncated after 106621. * In the same vein, Mersenne.org lets you get a listing of all factors found after a given date, so a private mirror of data can be kept uptodate easily, but Mersenne.ca does not provide a way to do this. * Mersenne.org only maintains data for factors of exponents below 1.000 billion, but Mersenne.ca records them for exponents below 2^{32} ≈ 4.29 billion. Maybe Mersenne.org could consider adopting the higher limit and incorporating the Mersenne.ca data, this would make that data more secure and accessible. Last fiddled with by GP2 on 20160611 at 17:52 
20160611, 21:58  #2  
Sep 2006
Brussels, Belgium
66F_{16} Posts 
Quote:
I would prefer to have all factors or an indication that a Mersenne number is fully factored.... Jacob 

20160611, 22:20  #3 
"James Heinrich"
May 2004
exNorthern Ontario
2×1,621 Posts 
The composite factor (which was found via P1) for M499211 is just over 200 bits, which is actually a cutoff point in the factoring code beyond which it was supposed to fall back to a probableprime test rather than attempting to fully factor the number, but the PRP section was commentedout for whatever reason. I have reenabled it, and removed the composite factor for M48152443, M63323077, M71099111, M72051011, M77999869.
To clarify, up until mid2015 mersenne.ca accepted factors independently from mersenne.org and generally required people to submit results in two places. But for the last year or so mersenne.ca does not accept any results submissions below 1000M, that data is all pulled from mersenne.org From the time when factors could be submitted directly to mersenne.ca it is entirely possible that mersenne.ca might have some additional factors for alreadyfactored exponents that mersenne.org doesn't have, especially since in times past mersenne.org was sometimes reluctant to accept additional factors once an exponent had a factor (this has been changed in the past few months). If you would like to "harvest" data from mersenne.ca, either oneoff or an ongoing basis, let me know and I'm sure I can make something available. Let me know what kind of format and data you would find useful. 
20160612, 01:05  #4 
Aug 2002
Buenos Aires, Argentina
3^{2}·149 Posts 
I found that factor. While trying to find factors of known composite Mersenne numbers, I ran P1 for all exponents 900k to 1M with bounds B1=200K, B2=5M on September 2014 and then with bounds B1=1M, B2=30M on May and June 2015.

20160612, 11:07  #5  
Sep 2003
3^{2}·7·41 Posts 
Quote:


20160612, 11:23  #6  
Sep 2003
5027_{8} Posts 
Quote:
How were those results submitted, and did you actually manually submit the results to mersenne.ca? The most alarming scenario would be if you only submitted results to mersenne.org (PrimeNet), which mersenne.ca automatically mirrored as it normally does, and then at some later date the result was somehow dropped from mersenne.org... Do you still have the results.txt or prime.log files that show how the communication with PrimeNet went for that factor? Last fiddled with by GP2 on 20160612 at 11:45 

20160612, 14:31  #7  
"James Heinrich"
May 2004
exNorthern Ontario
2·1,621 Posts 
Quote:
I would be extremely surprised if that was the case. I can't think of a scenario that would cause that to happen. 

20160613, 02:59  #8  
Aug 2002
Buenos Aires, Argentina
3^{2}·149 Posts 
Quote:
I tried to send the results to both sites, but since it was a manual method, sometimes I sent the results to only one site. At that moment mersenne.org did not store P1 results when no factors were found. In March 2016, I sent all my results again (except from that notebook that was broken) to mersenne.org. Madpoo found that in that batch there were some factors there were not submitted to mersenne.org. 

20160613, 16:11  #9  
Serpentine Vermin Jar
Jul 2014
6323_{8} Posts 
Quote:


20160614, 03:38  #10  
Sep 2003
3^{2}×7×41 Posts 
Quote:
First of all, ignore the dateandtimestamps when comparing the two sets of data, they don't really match up. New missing factors (I have NOT manually added these). Looks like a whole contiguous batch got dropped at 2.3M: Code:
1076263,404746441851288671009, 1098373,6204639949258669231, 2323939,34907963344957585217, 2324149,10662161439784221823, 2324381,107863054869879369583, 2325181,318915542216651018294231, 2326673,39761566392781203343, 2327099,6427615260255940157417, 2327197,48412896678190509306913, 2327539,8551967281381645001, 2327723,102168863356731488671, 2328707,153988958336242699849, 2328857,6950280843227472409, 2329387,27469302986377283377, 2330099,841016607230679811999, 2330753,14911860910792507153, 2330959,381327229728174339871, 2331047,342543153937917186103, 2331089,52826547962123945702729, 2332313,10541466616863208896809, 2332321,973275814636083173617, 2332373,7967296408733560193, 2332607,6598886445226817393, 2332969,4838699545847273809, 2334139,69752916382675135647606529, 2334301,12054961403420760459737, 7012337,10211694487439188129, These factors occur twice for some reason (shows up in the Detailed Reports  Factors Found). Mathematically each factor of a Mersenne number with prime exponent can never be a factor of any other Mersenne number with prime exponent, so maybe the database could create a unique index on the factor field: Stuff mentioned in my previous post: Missing factors for 100003 and 954257, which I already manually added to mersenne.org: Code:
100003,1113838336566049330755578765857, 954257,44522862069024324027649, Code:
499211,2253474049908052340696986104536103562940922999791841767712473, Code:
100,11, 77777,127, 77777,799993, 77777,595460713, 77777,17137716527, 77777,1398731345881, 77777,60685647225571918873, Last fiddled with by GP2 on 20160614 at 04:18 

20160614, 05:55  #11 
Sep 2003
3^{2}·7·41 Posts 
New missing factors in the range 10M to 20M, I did NOT manually report these:
Code:
10308371,32121976624860440209, 12540691,119576888298349980161, 12667997,5380033915595933471, 14124091,14646676110705643369, 14138779,4420795284601927577, 14160401,13389566679935929601, 14295341,4804614434819289553, 14315201,12085443174681846961, 14554649,5609714823499434887, 15186349,8599602188387049841, Also, as mentioned in the previous post, 10504531 has a trailing space when you select "Print simple text report" in the Detailed Reports  Factors Found report: Code:
10504531,28700796788611131118633 , Last fiddled with by GP2 on 20160614 at 05:55 
Thread Tools  
Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
ECM on small Mersenne Numbers  Erich  PrimeNet  16  20120929 23:08 
Can two Mersenne numbers share a factor?  James Heinrich  Math  57  20110912 14:16 
mersenne prime as a factor of another number  kurtulmehtap  Math  21  20101108 18:21 
Mersenne factor  bitblit  Math  3  20090502 01:20 
Fast calculations modulo small mersenne primes like M61  Dresdenboy  Programming  10  20040229 17:27 