This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A127581 #7 Oct 19 2017 03:15:06
%S A127581 2,3,7,23,31,127,127,383,1279,3583,5119,6143,8191,73727,81919,131071,
%T A127581 131071,524287,524287,14680063,14680063,14680063,109051903,109051903,
%U A127581 654311423,738197503,738197503,2147483647,2147483647,2147483647
%N A127581 Smallest prime of the form k*2^n - 1, for k >= 2.
%F A127581 a(n) << 37^n by Xylouris' improvement to Linnik's theorem. - _Charles R Greathouse IV_, Dec 10 2013
%e A127581 a(3)=23 because 23 = 3*2^3 - 1 is prime.
%e A127581 a(4)=31 because 31 = 2*2^4 - 1 is prime.
%t A127581 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 A127581 Cf. A007522, A127575-A127582, A127586-A127587.
%K A127581 nonn
%O A127581 0,1
%A A127581 _Artur Jasinski_, Jan 19 2007
%E A127581 Edited by _Don Reble_, Jun 11 2007