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 A270644 #9 Oct 09 2020 10:42:53
%S A270644 1,2,2,2,1,2,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,1,1,
%T A270644 2,2,1,2,1,1,2,1,2,2,1,1,2,1,1,2,1,2,2,1,2,1,1,2,2,1,2,2,1,2,1,1,2,1,
%U A270644 1,2,2,1,2,1,1,2,1,2,2,1,2,2,1,1,2,1
%N A270644 The sequence a of 1's and 2's starting with (1,2,2,2) such that a(n) is the length of the (n+2)nd run of a.
%C A270644 See A270641 for a guide to related sequences.
%H A270644 Clark Kimberling, <a href="/A270644/b270644.txt">Table of n, a(n) for n = 1..10000</a>
%e A270644 a(1) = 1, so the 3rd run has length 1, so a(5) must be 1 and a(6) = 2.
%e A270644 a(2) = 2, so the 4th run has length 2, so a(7) = 2 and a(8) = 1.
%e A270644 a(3) = 2, so the 5th run has length 2, so a(9) = 1and a(10) = 2.
%e A270644 Globally, the runlength sequence is 1,3,1,2,2,2,1,2,2,1,1,2,2,1,2,2,..., and deleting the first 2 terms leaves the same sequence.
%t A270644 a = {1, 2, 2, 2}; Do[a = Join[a, ConstantArray[If[Last[a] == 1, 2, 1], {a[[n]]}]], {n, 200}]; a (* _Peter J. C. Moses_, Apr 01 2016 *)
%Y A270644 Cf. A000002, A006928, A022300, A270641.
%K A270644 nonn,easy
%O A270644 1,2
%A A270644 _Clark Kimberling_, Apr 06 2016