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 A026370 #4 Mar 30 2012 18:56:06 %S A026370 1,2,3,1,4,5,2,6,7,3,8,9,10,11,4,12,13,5,14,15,16,17,6,18,19,7,20,21, %T A026370 22,23,8,24,25,9,26,27,10,28,29,11,30,31,32,33,12,34,35,13,36,37,38, %U A026370 39,14,40,41,15,42,43,16,44,45,17,46,47,48,49 %N A026370 a(n) = a(m) if a(m) has already occurred exactly once and n = a(m)+2m+1, else a(n) = least positive integer that has not yet occurred. %K A026370 nonn %O A026370 1,2 %A A026370 _Clark Kimberling_