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 A135979 #14 Sep 29 2018 10:40:48
%S A135979 5,9,12,13,17,19,23,25,26,27,29,32,33,34,35,39,45,46,49,53,57,58,60,
%T A135979 62,69,74,75,82,88,93,99,129,140,152,164,166,168,178,179
%N A135979 Indices n such that 2^prime(n)-1 has exactly 2 distinct prime factors.
%C A135979 a(40)>=206. - _Amiram Eldar_, Sep 29 2018
%F A135979 Equals {k: A001221(A001348(k)) = 2}. a(n) = A049084(A135978(n)). - _R. J. Mathar_, May 03 2008
%t A135979 k = {}; Do[If[ ! PrimeQ[2^Prime[n] - 1], c = FactorInteger[2^Prime[n] - 1]; d = Length[c]; If[d == 2, AppendTo[k, n]]], {n, 1, 40}]; k
%t A135979 Select[Range[40],PrimeNu[2^Prime[#]-1]==2&] (* _Harvey P. Dale_, Jul 07 2013 *)
%Y A135979 Cf. A000225, A065341, A054723, A134852, A135975, A135976, A135977, A135978.
%K A135979 nonn,more
%O A135979 1,1
%A A135979 _Artur Jasinski_, Dec 09 2007
%E A135979 Edited by _R. J. Mathar_, May 03 2008
%E A135979 a(17)-a(34) from _Donovan Johnson_, Jun 14 2009
%E A135979 a(35)-a(39) from _Amiram Eldar_, Sep 29 2018