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 A031320 #4 Mar 30 2012 18:56:23 %S A031320 4,13,23,33,43,53,63,66,68,70,72,73,74,83,93,107,122,137,152,167,182, %T A031320 197,202,205,208,211,212,214,227,242,257,272,287,302,317,332,347,352, %U A031320 355,358,361,362,364,377,392,407,422,437,452 %N A031320 Position of n-th 7 in A031312. %K A031320 nonn %O A031320 1,1 %A A031320 _Clark Kimberling_