mersenneforum.org Primo quit with "Candidate is presumably a square"
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2011-06-07, 07:31   #1
lavalamp

Oct 2007
Manchester, UK

53F16 Posts
Primo quit with "Candidate is presumably a square"

Hi there, I'm hoping someone could help me with Primo. I have a 2368 digit probable prime, but Primo aborts a few seconds into the certification with the status "Candidate is presumably a square". It does not give any indication as to why it is presumably a square.

The number is the least common multiple of all the integers from 1 to 5449, plus 1:
lcm(1, 2, ... 5449) + 1

I have found further terms for the related sequences A049536 and A049537 on OEIS, and wish to prove them prime, Primo however has other plans.

I have uploaded the .in file for anyone who wishes to try it, I have had to add the additional extension .txt to appease the forum, so that will need to be removed first.
Attached Files
 5449-plus.in.txt (2.3 KB, 105 views)

 2011-06-07, 07:42 #2 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 3×31×101 Posts Indeed, it does, and indeed it is not a square! Try the linux alpha version? It is different and may be free of this bug?
 2011-06-07, 08:44 #3 lavalamp     Oct 2007 Manchester, UK 17×79 Posts Ah, I was hoping I could just invert the polarity of something in a config file to fix it. I'm afraid I occupy a Linux free zone. Nevertheless, I have been trying to do something very Linuxy on Windows, which is to say compiling GMP-ECPP. Unfortunately I understand very little of the process and am being prevented from doing so by 2 errors and 2 warnings.
 2011-06-07, 08:53 #4 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 222618 Posts Code: /m/ECPP> ./atkin235.gmp-5.0.1 random seed = 1307956510 error_shift = 1000 precision = 10000 total = 3183 max = 111763 PI = 3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651328230... number to be tested: 4651492098832669839577282545688156677339445061279465845249031751238423754923388468675292837260397395471135746890874769... Bmax = 2000 #-- We are sinking! We are sinking! #-- Errh... What ...are you 'sinking about? (it seems to be thinking about something... we'll see)
 2011-06-08, 03:07 #5 lavalamp     Oct 2007 Manchester, UK 17×79 Posts A friend on Linux tried the new 4.0.0 alpha 6 version of Primo and got the same error. Would this be worth contacting the developers about? We also both got quite stuck trying to compile ECPP. How did your build of ECPP do Batalov, did it fail on this number or was it making progress?
 2011-06-08, 03:27 #6 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 3·31·101 Posts It is măil at ęllipšă dot ęü and Marcel is a very nice guy. P.S. GMP-ECPP process is still running but I haven't redirected its output so I will not have a certificate - only will tell you if/when it will finish. Primo would have finished by now. I simply built as per the source instructions - a single line, no makefile, prereq: need -lgmpxx (which has the C++ binidings, I gather) and -lgmp. Last fiddled with by Batalov on 2011-06-08 at 03:44 Reason: (obfuscating email against robots)
 2011-06-08, 10:59 #7 akruppa     "Nancy" Aug 2002 Alexandria 1001101000112 Posts
 2011-06-08, 11:11 #8 lavalamp     Oct 2007 Manchester, UK 101001111112 Posts My friend on Ubuntu got ECPP compiled (with -o3), and did a test on a small number. Unfortunately, even on a faster CPU, GMP-ECPP was approximately 210 times slower than Primo (2.26 GHz i3 vs 1.7 GHz P4). I'm not sure if that's normal, it seems a pretty large factor to be slower by. It would turn a few hours of computation into a couple of months.
 2011-06-08, 22:36 #9 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 939310 Posts I've finished a proof for 10^999+7 with ECPP thing, and indeed it is very slow. Primo on the same number took 22 minutes, ECPP took almost 10 hours. The size dependence for both algos should be O(digits4+o(1)), so it looks pretty bleak for even a 2700-digit number. Do write to Marcel; he will be happy to fix this small problem, I think.
 2011-06-08, 23:35 #10 lavalamp     Oct 2007 Manchester, UK 17·79 Posts I did email Marcel, he has now fixed the Linux version. I have inquired further about whether the Windows version will also receive the fix.
 2011-06-09, 01:59 #11 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 3×31×101 Posts And off it goes using four threads if you'd need it... Should be pretty fast.

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