20180916, 18:07  #1 
Aug 2018
5 Posts 
Prime95 finding any prime?
Hello Prime95 can you help me I want to find any prime number?
What can I do if I want to find eg, 23 is a prime number ? 
20180916, 18:35  #2 
"Curtis"
Feb 2005
Riverside, CA
2×5×11×43 Posts 
To determine 23 is prime, try dividing by every prime below the square root of 23.
2 and 3 do not divide 23, so 23 is prime. 
20180917, 08:53  #3 
Nov 2016
B04_{16} Posts 

20180917, 12:10  #4 
Romulan Interpreter
Jun 2011
Thailand
9364_{10} Posts 

20180918, 10:40  #5 
Mar 2015
Australia
2×41 Posts 
Ha! (19:57) gp > (3411)!%341 %54 = 0 Andrew When in doubt, use Wilson's Theorem http://fredrikj.net/blog/2012/03/fac...lsonstheorem/ 
20180921, 10:48  #6 
Romulan Interpreter
Jun 2011
Thailand
2^{2}×2,341 Posts 
haha, you made my day!
You have however a mistake in the post: you must not say "Ha!", but "" (and don't tell me you made 54 trials to get that right! ) Last fiddled with by LaurV on 20180921 at 10:49 
20180924, 12:16  #7 
Mar 2015
Australia
122_{8} Posts 
I'm not sure how to respond, but anyway! I used a few trials, but not that many!
It was interesting exploring how far I could push this test, I got over 1000 but then needed to increase the stack limit in gp so gave up! Main point of my post was the link I shared. Frederik Johansson is the main aurthor of MPMath, Arb, and has made contributions to a number of other mathematical software projects. He made optimisations which let him test Wilson's Theorem up to 15 digits, that's crazy!! Andrew 
20180926, 21:48  #8 
Bemusing Prompter
"Danny"
Dec 2002
California
2^{3}×3^{3}×11 Posts 
I'm not sure I this answers your question, but Prime95 can only test numbers of the form 2^{p}  1 for primality.

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