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 A290200 #9 Jul 23 2017 21:53:26 %S A290200 2,5,17,257,65537 %N A290200 Prime numbers of the form 4^k + 1. %C A290200 Similar to Fermat primes, A019434, a(n) is of the form (2^2)^k + 1. %t A290200 Select[4^Range[0, 100] + 1, PrimeQ] %Y A290200 Cf. A019434, A092506. %K A290200 nonn,more %O A290200 1,1 %A A290200 _Robert Price_, Jul 23 2017