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 A088569 #21 Mar 16 2019 17:44:02
%S A088569 1,1,2,2,1,2,1,1,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2,1,1,2,2,1,2,2,1,2,1,
%T A088569 1,2,1,1,2,2,1,2,1,1,2,1,2,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,1,1,2,2,1,
%U A088569 2,2,1,2,1,1,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2
%N A088569 Anti-Kolakoski sequence (sequence of run lengths never coincides with the sequence itself).
%C A088569 Unique infinite word defined on alphabet {1,2} satisfying: a(1)=1, if a(n)=2 length of n-th run is 1, if a(n)=1 length of n-th run is 2. Kolakoski sequence satisfies the opposite definition: K(1)=1, if K(n)=2 length of n-th run is 2, if K(n)=1 length of n-th run is 1.
%C A088569 Equals A049705 without the first term. - _Jean-Christophe Hervé_, Nov 10 2014
%F A088569 a(n) = 3 - A000002(n+1) = A049705(n+1).
%e A088569 a(1)=1 hence first run must have length 2 and necessarily a(2)=1. Now second run must also have length 2 and therefore a(3) = a(4) = 2.
%Y A088569 Cf. A000002, A049705.
%K A088569 nonn
%O A088569 1,3
%A A088569 _Benoit Cloitre_, Nov 17 2003