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 A104821 #3 Mar 30 2012 17:26:11 %S A104821 3,297,4,7,12,45,330,391,82,85,92,121,251,124,214,129,304,130,353,131, %T A104821 137,139,144,160,163,192,286,340,146,315,150,151,158,144,160,163,192, %U A104821 286,340,144,160,163,192,286,340,170,172,144,160,163,192,286,340,207 %N A104821 Positions of prime numbers A104820 in A104819. %F A104821 A104821(n)=Position[A104819, A104820(n)] %Y A104821 Cf. A104807, A104819, A104820. %K A104821 nonn,base %O A104821 1,1 %A A104821 _Zak Seidov_, Mar 27 2005