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 A031258 #4 Mar 30 2012 18:56:21 %S A031258 8,18,19,21,31,46,54,57,60,61,76,91,93,96,106,121,129,132,135,136,137, %T A031258 140,143,146,149,151,152,155,158,161,164,166,167,168,170,171,184,204, %U A031258 215,219,223,224,244,264,267,271,284,304,315 %N A031258 Position of n-th 4 in A031253. %K A031258 nonn %O A031258 1,1 %A A031258 _Clark Kimberling_