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2017-08-05, 15:58   #1838
VBCurtis

"Curtis"
Feb 2005
Riverside, CA

2×2,819 Posts

Quote:
 Originally Posted by paulunderwood There seems to be a discrepancy: http://primes.utm.edu/primes/page.ph...3806&deleted=1
Hrmm. Both were found by the same machine, a new low-end i3 desktop that hasn't had its case opened. Thanks for pointing this out- I'll run a double-check on another machine myself, as the compositeness test you linked indicated some roundoff errors.

 2017-08-05, 17:02 #1839 VBCurtis     "Curtis" Feb 2005 Riverside, CA 2·2,819 Posts A double-check on my i7-haswell (linux-sllr64) confirms compositeness. Next time I see the machine that found this "prime", I'll make sure I didn't transpose digits when I copied down the exponent; but that's pretty unlikely with 3 consecutive zeros.
 2017-08-06, 07:53 #1840 Trilo     "W. Byerly" Aug 2013 81*2^3174353-1 7·19 Posts Since we are on the subject of consecutive large primes with small n gaps, here is a pair I found a while back: 1423*2^2179023-1 1423*2^2178363-1 The most interesting thing about this pair is that the k value has very low nash weight of just 309. It would be interesting if we could define a function that takes in the gap size, nash weight, and n size and outputs another number representing the "rarity" of the pair.
 2017-09-18, 09:42 #1841 amphoria     "Dave" Sep 2005 UK 53308 Posts 49*2^4360869-1 (1312755 digits) 49*2^4365175-1 (1314051 digits)
2017-09-18, 09:52   #1842
Thomas11

Feb 2003

27×3×5 Posts

Quote:
 Originally Posted by amphoria 49*2^4360869-1 (1312755 digits) 49*2^4365175-1 (1314051 digits)
Congratulations on this very nice pair, Dave!

 2017-09-20, 09:04 #1843 Kosmaj     Nov 2003 2×1,811 Posts Hi Dave, Congrats on nice primes! Congrats also to Trilo on his pair.
 2017-12-13, 20:19 #1844 Chair Zhuang   Dec 2017 128 Posts How long did your computer take to test it? And how many GHz has your computer?
2017-12-14, 14:48   #1845
amphoria

"Dave"
Sep 2005
UK

23×347 Posts

Quote:
 Originally Posted by Chair Zhuang How long did your computer take to test it? And how many GHz has your computer?
The first took 6300s to test on a 3.6 GHz Ivy Bridge CPU. The second was tested on a 2.9 GHz Haswell CPU. I currently don't have access to the timing but given that it has AVX2, I would expect it to be at least as fast as the other despite the lower clock speed.

 2017-12-15, 22:58 #1846 Chair Zhuang   Dec 2017 10102 Posts Thank you! amphoria. I am a new member.
 2017-12-18, 22:22 #1847 VBCurtis     "Curtis" Feb 2005 Riverside, CA 2·2,819 Posts 229*22581111-1 is prime. 776995 digits.
 2017-12-30, 10:40 #1848 Thomas11     Feb 2003 78016 Posts From our 7th drive: 2715*2^1629931-1 (490662 digits) 2715*2^1640137-1 (493734 digits)

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