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 A249858 #12 Aug 05 2019 14:38:11 %S A249858 0,0,0,1,0,1,2,1,2,3,0,3,4,0,4,5,1,2,6,1,5,6,3,7,8,0,8,9,0,9,10,0,5, %T A249858 11,1,9,12,1,6,13,2,11,14,4,14,15,2,15,12,5,16,17,3,17,18,0,18,19,0, %U A249858 19,20,0,19,21,1,15,22,3,17,22,4,19,24,2,21,25,3 %N A249858 a(n) = A249857(n) - A249856(n). %o A249858 (Haskell) %o A249858 a249858 n = a249857 n - a249856 n %Y A249858 Cf. A249856, A249857. %K A249858 nonn %O A249858 1,7 %A A249858 _Reinhard Zumkeller_, Nov 09 2014