

A270643


The sequence a of 1's and 2's starting with (1,2,2,1) such that a(n) is the length of the (n+3)rd run of a.


2



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, 1
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OFFSET

1,2


COMMENTS

See A270641 for a guide to related sequences.


LINKS

Clark Kimberling, Table of n, a(n) for n = 1..10000


EXAMPLE

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


MATHEMATICA

a = {1, 2, 2, 1}; Do[a = Join[a, ConstantArray[If[Last[a] == 1, 2, 1], {a[[n]]}]], {n, 200}]; a (* Peter J. C. Moses, Apr 01 2016 *)


CROSSREFS

Cf. A000002, A006928, A022300, A270641.
Sequence in context: A088424 A317960 A270642 * A270647 A261126 A097456
Adjacent sequences: A270640 A270641 A270642 * A270644 A270645 A270646


KEYWORD

nonn,easy


AUTHOR

Clark Kimberling, Apr 06 2016


STATUS

approved



