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 A023631 #4 Mar 30 2012 18:55:53 %S A023631 1,4,6,7,10,11,15,16,18,19,23,24,26,27,29,30,34,35,39,40,42,43,45,46, %T A023631 50,51,55,56,60,61,63,64,66,67,71,72,74,75,77,78,82,83,87,88,92,93,95, %U A023631 96,98,99,103,104,106,107,109,110,114,115,117,118,120,121,125 %N A023631 a(n) = c([ (n+1)/2 ]) + n, with a(1) = 1 and a(2) = 4, c = complement to a. %K A023631 nonn %O A023631 1,2 %A A023631 _Clark Kimberling_