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 A031039 #4 Mar 30 2012 18:56:20 %S A031039 3,15,31,40,42,44,46,47,48,50,52,54,63,79,95,111,131,155,179,193,196, %T A031039 199,202,203,205,208,211,214,227,251,275,299,323,347,371,385,388,391, %U A031039 394,395,397,400,403,406,419,443,467,491,504 %N A031039 Position of n-th 3 in A031035. %K A031039 nonn %O A031039 1,1 %A A031039 _Clark Kimberling_