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 A026251 #4 Mar 30 2012 18:56:05 %S A026251 2,4,2,6,8,4,10,12,14,6,16,18,8,20,22,24,10,26,28,12,30,32,14,34,36, %T A026251 38,16,40,42,18,44,46,48,20,50,52,22,54,56,24,58,60,62,26,64,66,28,68, %U A026251 70,72,30,74,76,32,78,80,82,34,84,86,36,88,90 %N A026251 a(n) = |s(n) - n|, where s = A026250. Also a(n) = 2*t(n), where t = A026249. %K A026251 nonn %O A026251 1,1 %A A026251 _Clark Kimberling_