A270646 - OEIS

%I #14 Oct 09 2020 10:43:03

%S 2,2,1,1,2,2,1,1,2,1,2,2,1,1,2,1,2,2,1,2,2,1,1,2,1,2,2,1,2,2,1,1,2,1,

%T 1,2,2,1,2,1,1,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2,1,1,2,2,1,2,2,1,2,1,1,

%U 2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,1,1

%N The sequence a of 1's and 2's starting with (2,2,1,1) such that a(n) is the length of the (n+2)nd run of a.

%C See A270641 for a guide to related sequences.

%C a(1) = 2, so the 3rd run has length 2, so a(5) must be 2 and a(6) = 1.

%C a(2) = 2, so the 4th run has length 2, so a(7) = 1 and a(8) = 1.

%C a(3) = 1, so the 5th run has length 1, so a(9) = 2 and a(10) = 1.

%C Globally, the runlength sequence of a is 2,2,2,2,1,1,2,2,1,1,2,1,2,2,1,1,2,..., and deleting the first 2 terms leaves a = A270646.

%H Clark Kimberling, <a href="/A270646/b270646.txt">Table of n, a(n) for n = 1..10000</a>

%t a = {2,2,1,1}; 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