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Old 2017-08-10, 13:47   #4
paulunderwood
 
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Sep 2002
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Quote:
Originally Posted by Dr Sardonicus View Post
The question of when 2^n - 3 alone might be prime may be of some interest in its own right. It wouldn't surprise me at all if someone had compiled a factor table for n into the hundreds, and a list of pseudoprimes for larger n's.
http://www.primenumbers.net/prptop/s...&action=Search

I was interested in 2-PRP being enough for these PRPs. In general 2^n-2^k-1. Most general a-PRP for:

"For integers a>1, s>=0, all r>0, all t>0, odd and irreducible {a^s\times\prod{(a^r-1)^t}}-1 is a-PRP, except for the cases a^2-a-1 and a-2 and a-1 and -1."

This includes a^2-2, for which I have done a cursory check for a < 10^13.

Last fiddled with by paulunderwood on 2017-08-10 at 13:53
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