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.

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, 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, 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1

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 3rd run has length 1, so a(5) must be 1 and a(6) = 2.
a(2) = 2, so the 4th run has length 2, so a(7) = 2 and a(8) = 1.
a(3) = 2, so the 5th run has length 2, so a(9) = 1and a(10) = 2.
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.

Mathematica

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 *)

Crossrefs

Cf. A000002, A006928, A022300, A270641.

Sequence in context: A136690 A144703 A276825 * A361156 A097026 A189225

Adjacent sequences: A270641 A270642 A270643 * A270645 A270646 A270647

Keyword

nonn,easy

Author

Clark Kimberling, Apr 06 2016

Status

approved