Timeline for Find the largest prime whose length, sum and product is prime
Current License: CC BY-SA 3.0
12 events
| when toggle format | what | by | license | comment | |
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| Jun 17, 2020 at 9:04 | history | edited | CommunityBot |
Commonmark migration
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| Jul 31, 2014 at 23:13 | history | edited | Charles | CC BY-SA 3.0 |
alternate approach
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| Jul 31, 2014 at 20:47 | comment | added | Charles | @isaacg: I'll do that once I've found a prime with the new code. I wouldn't feel right posting an answer without results. | |
| Jul 31, 2014 at 20:46 | comment | added | isaacg | You can probably outsource the run to a faster computer by posting it here - I'd try, but I'm not sure my computer is that fast either. | |
| Jul 31, 2014 at 20:45 | comment | added | Charles | @isaacg: Slow computer, slight efficiency loss to interpreting the GP code, not the greatest algorithms for big numbers (esp. since it's 32-bit not 64). I get to avoid #2 and #3 with the pfgw code. We'll see if I bit off more than I can chew with 10,000. | |
| Jul 31, 2014 at 20:40 | comment | added | isaacg | That's some impressive speed. The solution you posted above is about 50% slower than my solution, for comparison. | |
| Jul 31, 2014 at 20:31 | comment | added | Charles | @isaacg: In any case I'm working on the "better solution" I mentioned now: pushing the hard work to pfgw. It's searched the first 20 pairs above 10^10000 without finding anything but that only took ~15 minutes. | |
| Jul 31, 2014 at 20:28 | comment | added | Charles | @isaacg: Maybe so. My heuristics are clearly off, since I would have expected probability ~80% to find a prime in a given pair: 1 - exp(-15/(4*log 10)), but they seem to be rarer than that, so they don't act like random {2, 3, 5}-smooth numbers of their size (unless I goofed the calculation). | |
| Jul 31, 2014 at 20:23 | comment | added | isaacg | No, actually, you were incredibly lucky. (4127,3) is the first pair after 4100, and by pure chance it happens to have a prime. A lot of pairs have no prime at all. | |
| Jul 31, 2014 at 20:15 | comment | added | Charles | @isaacg: I was just trying to be larger than the (incorrect) Mathematica solution, which was just over 4000. I just went to the next multiple of 100 as a 'nothing-up-my-sleeve' number. Actually it seems that this was an unfortunate starting place, since I had to go longer than I expected (and longer than Mathematica!) to find a prime. | |
| Jul 31, 2014 at 20:10 | comment | added | isaacg | How did you know to start at 4100? | |
| Jul 31, 2014 at 18:47 | history | answered | Charles | CC BY-SA 3.0 |