A270646 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.

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

Offset

1,1

Comments

See A270641 for a guide to related sequences.

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

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

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

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.

Links

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

Mathematica

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 *)

Crossrefs

Cf. A000002, A006928, A022300, A270641.

Sequence in context: A286944 A026605 A331104 * A293540 A073783 A134430

Adjacent sequences: A270643 A270644 A270645 * A270647 A270648 A270649

Keyword

nonn,easy

Author

Clark Kimberling, Apr 07 2016

Status

approved