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 A057516 #7 May 14 2020 05:09:17 %S A057516 0,0,1,0,2,1,1,0,0,3,2,2,1,1,2,1,1,0,0,1,0,0,0,4,3,3,2,2,3,2,2,1,1,2, %T A057516 1,1,1,3,2,2,1,1,2,1,1,0,0,1,0,0,0,2,1,1,0,0,1,0,0,0,1,0,0,0,0,5,4,4, %U A057516 3,3,4,3,3,2,2,3,2,2,2,4,3,3,2,2,3,2,2,1,1,2,1,1,1,3,2,2,1,1,2,1,1,1,2,1,1 %N A057516 Number of sea-level valleys in Catalan mountain ranges encoded by A014486. %F A057516 a(0) = 0, a(n) = card(binexp2pars(A014486(n)))-1 = A057515(n)-1. %Y A057516 Cf. A057514. %K A057516 nonn %O A057516 0,5 %A A057516 _Antti Karttunen_, Sep 03 2000