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 A138647 #5 Nov 21 2013 12:49:20
%S A138647 521,11293772630057337854244300009061892827351888021,
%T A138647 6573840876841765045097738044023218580610053625908525039752324422200521,
%U A138647 164346021921044126127443451100580464515251340647713125993808110555013021
%N A138647 Primes of form (5^n+1)/6.
%t A138647 a={};Do[x=(5^n+1)/6;If[PrimeQ[x],AppendTo[a,x]],{n,0,12^2}];a
%t A138647 Select[(5^Range[0,200]+1)/6,PrimeQ] (* _Harvey P. Dale_, Jul 18 2011 *)
%K A138647 nonn
%O A138647 1,1
%A A138647 _Vladimir Joseph Stephan Orlovsky_, May 15 2008