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 A031091 #4 Mar 30 2012 18:56:20 %S A031091 3,15,33,46,48,50,51,52,54,56,58,60,62,69,87,105,123,141,162,189,216, %T A031091 235,238,241,243,244,247,250,253,256,259,270,297,324,351,378,405,432, %U A031091 459,478,481,484,486,487,490,493,496,499,502 %N A031091 Position of n-th 3 in A031087. %K A031091 nonn %O A031091 1,1 %A A031091 _Clark Kimberling_