%I #9 Feb 25 2020 10:30:37
%S 2,2,4,3,4,5,1,6,1,5,4,3,6,5,9,7,4,5,15,19,4,27,4,12,6,38,30,5,27,13,
%T 15,2,10,7,4,7,9,32,10,2,10,33,10,2,75,17,4,5,6,12,21,6,150,14,7,11,
%U 30,27,51,29,70,58,10,10,37,45,79,212,177,17,4,33,16,54,24,20,222,105,9,83,10
%N Least k such that k*(2^n)*((2^n-1)^2) - 1 is a prime number.
%H P. CAMI, <a href="/A171580/b171580.txt">Table of n, a(n) for n = 1..5000</a>
%o (PARI) a(n) = for(k=1, oo, if(ispseudoprime(k*(2^n)*((2^n-1)^2)-1), return(k))); \\ _Jinyuan Wang_, Feb 25 2020
%K nonn
%O 1,1
%A _Pierre CAMI_, Dec 12 2009
%E Extended by _Ray Chandler_, Dec 19 2009