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 A020239 #16 Apr 25 2016 11:45:27
%S A020239 85,1099,5149,7107,8911,9637,13019,14491,17803,19757,20881,22177,
%T A020239 23521,26521,35371,44173,45629,54097,56033,57205,75241,83333,85285,
%U A020239 86347,102719,110309,153401,184339,191959,222529,242845,253021,253927,269861
%N A020239 Strong pseudoprimes to base 13.
%H A020239 R. J. Mathar, <a href="/A020239/b020239.txt">Table of n, a(n) for n = 1..668</a>
%H A020239 <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>
%o A020239 (PARI) /* insert A001262 code here */
%o A020239 isA020239(n)={
%o A020239 isStrongPsp(n,13)
%o A020239 }
%o A020239 {
%o A020239 for(n=1,10000000000, if(isA020239(n), print(n) ;) ;) ;
%o A020239 } /* _R. J. Mathar_, Mar 07 2012 */
%K A020239 nonn
%O A020239 1,1
%A A020239 _David W. Wilson_