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 A137992 #10 Feb 01 2015 23:00:18
%S A137992 1,2,1,0,2,2,2,2,1,0,2,0,1,2,2,2,2,2,2,2,2,2,2,2,2,2,1,0,2,0,1,2,2,2,
%T A137992 2,0,1,2,1,0,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
%U A137992 2,2,2,2,2,2,2,2,2,2,2,2
%N A137992 A014137 (= partial sums of Catalan numbers A000108) mod 3.
%C A137992 As usual, "mod 3" means to choose the unique representative in { 0,1,2 } of the equivalence class modulo 3Z.
%F A137992 a(n) = sum( k=0..n, C(k) ) (mod 3), where C(k) = binomial(2k,k)/(k+1).
%F A137992 a(n) = 1 <=> n = 2 A137821(m) for some m (with A137821(0)=0).
%o A137992 (PARI) A137992(n) = lift( sum( k=0,n, binomial( 2*k,k )/(k+1), Mod(0,3) ))
%Y A137992 Cf. A014137, A000108, A137821-A137824, A107755; A014138(n)+1 = a(n+1) (mod 3).
%K A137992 easy,nonn
%O A137992 0,2
%A A137992 _M. F. Hasler_, Mar 16 2008