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A127581 Smallest prime of the form k*2^n - 1, for k >= 2. 17

%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, A127575-A127582, A127586-A127587.

%K nonn

%O 0,1

%A _Artur Jasinski_, Jan 19 2007

%E Edited by _Don Reble_, Jun 11 2007

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Last modified May 21 10:48 EDT 2019. Contains 323443 sequences. (Running on oeis4.)