%I
%S 2,3,7,23,31,127,127,383,1279,3583,5119,6143,8191,73727,81919,131071,
%T 131071,524287,524287,14680063,14680063,14680063,109051903,109051903,
%U 654311423,738197503,738197503,2147483647,2147483647,2147483647
%N Smallest prime of the form k*2^n  1, for k >= 2.
%F a(n) << 37^n by Xylouris' improvement to Linnik's theorem.  _Charles R Greathouse IV_, Dec 10 2013
%e a(3)=23 because 23 = 3*2^3  1 is prime.
%e a(4)=31 because 31 = 2*2^4  1 is prime.
%t a = {}; Do[k = 1; While[ !PrimeQ[k 2^n + 2^n  1], k++ ]; AppendTo[a, k 2^n + 2^n  1], {n, 0, 50}]; a
%Y Cf. A007522, A127575A127582, A127586A127587.
%K nonn
%O 0,1
%A _Artur Jasinski_, Jan 19 2007
%E Edited by _Don Reble_, Jun 11 2007
