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%I #4 Apr 09 2016 16:27:46
%S 2,2,2,2,1,1,2,2,1,1,2,2,1,2,1,1,2,2,1,2,1,1,2,2,1,2,2,1,2,1,1,2,2,1,
%T 2,2,1,2,1,1,2,2,1,2,2,1,1,2,1,1,2,1,2,2,1,1,2,1,1,2,2,1,2,2,1,2,1,1,
%U 2,2,1,2,2,1,1,2,1,2,2,1,2,1,1,2,1,1
%N The sequence a of 1's and 2's starting with (2,2,2,2) such that a(n) is the length of the (n+1)st run of a.
%C See A270641 for a guide to related sequences.
%H Clark Kimberling, <a href="/A270648/b270648.txt">Table of n, a(n) for n = 1..10000</a>
%e a(1) = 2, so the 2nd run has length 2, so a(5) must be 1 and a(6) = 1.
%e a(2) = 2, so the 3rd run has length 2, so a(7) = 2 and a(8) = 2.
%e a(3) = 2, so the 4th run has length 2, so a(9) = 1 and a(10) = 1.
%e Globally, the runlength sequence of a is 4,2,2,2,2,1,1,2,2,1,1,2,2,1,2,1,1,2,..., and deleting the first term leaves a = A270648.
%t a = {2,2,2,2}; Do[a = Join[a, ConstantArray[If[Last[a] == 1, 2, 1], {a[[n]]}]], {n, 200}]; a (* _Peter J. C. Moses_, Apr 01 2016 *)
%Y Cf. A000002, A006928, A022300, A270641.
%K nonn,easy
%O 1,1
%A _Clark Kimberling_, Apr 07 2016
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