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 A031081 #4 Mar 30 2012 18:56:20 %S A031081 4,18,36,54,63,65,67,69,71,72,73,75,77,79,90,108,126,144,167,194,221, %T A031081 248,262,265,268,271,274,275,277,280,283,286,302,329,356,383,410,437, %U A031081 464,491,505,508,511,514,517,518,520,523,526 %N A031081 Position of n-th 4 in A031076. %K A031081 nonn %O A031081 1,1 %A A031081 _Clark Kimberling_