

A270642


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


2



1, 1, 2, 2, 1, 2, 1, 1, 2, 2, 1, 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, 1, 1, 2, 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, 2, 1, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1
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OFFSET

1,3


COMMENTS

See A270641 for a guide to related sequences.


LINKS



EXAMPLE

a(1) = 1, so the 3rd run has length 1, so a(5) must be 1.
a(2) = 1, so the 4th run has length 1, so a(6) = 2 and a(7) = 1.
a(3) = 2, so the 5th run has length 2, so a(8) = 1 and a(9) = 2.
a(4) = 2, so the 6th run has length 2, so a(10) = 2 and a(11) = 1.
Globally, the runlength sequence is 2,2,1,1,2,2,1,2,1,1,2,2,1,2,..., and deleting the first 2 terms leaves the same sequence.


MATHEMATICA

a = {1, 1, 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 *)


CROSSREFS



KEYWORD

nonn,easy


AUTHOR



STATUS

approved



