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 A138956 #5 Nov 21 2013 12:49:20
%S A138956 461,10501,2149818248341,20728082811027490541,
%T A138956 481868222983777875077033646523111996342381,
%U A138956 63774650109719491827977851592475862662743267652837460857617262084586443004114519194264814815101
%N A138956 Primes of the form (4^n + 5^n)/9.
%t A138956 a={}; Do[p=(4^n+5^n)/9; If[PrimeQ[p], AppendTo[a, p]], {n, 1, 12^2}];a
%t A138956 Select[Table[(4^n+5^n)/9,{n,160}],PrimeQ] (* _Harvey P. Dale_, Oct 22 2011 *)
%Y A138956 Cf. A128335.
%K A138956 nonn
%O A138956 1,1
%A A138956 _Vladimir Joseph Stephan Orlovsky_, May 16 2008