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 A216531 #18 May 02 2013 13:03:21
%S A216531 7,19,31,67,2137,268207
%N A216531 Numbers n such that (10^n + 1)/11 is prime and can be written in the form a^2 + 7*b^2.
%C A216531 These exponents are congruent to {0, 1, 3} mod 6.
%H A216531 Samuel S. Wagstaff, Jr. <a href="http://homes.cerias.purdue.edu/~ssw/cun/index.html">The Cunningham Project</a>
%Y A216531 Cf. A001562.
%K A216531 nonn
%O A216531 1,1
%A A216531 _V. Raman_, Sep 08 2012