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 A247260 #9 Sep 11 2014 15:13:04
%S A247260 1,2,4,17,136,147,203,590,754,964,970,1847,2031,2727,2871,5442,7035,
%T A247260 7266,11230,23307,27795,34152,42614,127206,133086
%N A247260 Numbers n such that 5*6^n + 1 is prime.
%C A247260 a(26) > 2*10^5.
%t A247260 Do[ If[ PrimeQ[5*6^n + 1], Print[n]], {n, 0, 200000}]
%o A247260 (PARI)
%o A247260 for(n=0,2*10^5,if(ispseudoprime(5*6^n+1),print1(n,", "))) \\ _Derek Orr_, Sep 10 2014
%Y A247260 Cf. A079906.
%K A247260 nonn,hard,more
%O A247260 1,2
%A A247260 _Robert Price_, Sep 10 2014