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 A300408 #21 Apr 03 2018 16:59:47
%S A300408 1217,19457,1337006139375617
%N A300408 Primes of the form 19*2^n + 1.
%C A300408 Next term a(4) = 19*2^366 + 1 > 10^111.
%C A300408 For the corresponding exponents n see A032359.
%H A300408 Ray Ballinger, Wilfried Keller, <a href="http://www.prothsearch.com/riesel1.html">List of primes k*2^n + 1 for k < 300</a>.
%p A300408 a:=(n,k)->`if`(isprime(k*2^n+1), k*2^n+1, NULL):
%p A300408 seq(a(n,19), n=1..366);
%o A300408 (GAP) Filtered(List([1..500],n->19*2^n + 1),IsPrime); # _Muniru A Asiru_, Mar 06 2018
%o A300408 (PARI) lista(nn) = {for(k=1, nn, if(ispseudoprime(p=19*2^k+1), print1(p, ", ")));} \\ _Altug Alkan_, Mar 29 2018
%Y A300408 Cf. A019434, A032359, A039687, A050527, A050528, A050529, A195745, A050526, A300406, A300407.
%K A300408 nonn,less
%O A300408 1,1
%A A300408 _Martin Renner_, Mar 05 2018