A270648 The sequence a of 1's and 2's starting with (2,2,2,2) such that a(n) is the length of the (n+1)st run of a.

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

Offset

1,1

Comments

See A270641 for a guide to related sequences.

Links

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

Example

a(1) = 2, so the 2nd run has length 2, so a(5) must be 1 and a(6) = 1.
a(2) = 2, so the 3rd run has length 2, so a(7) = 2 and a(8) = 2.
a(3) = 2, so the 4th run has length 2, so a(9) = 1 and a(10) = 1.
Globally, the runlength sequence of a is 4,2,2,2,2,1,1,2,2,1,1,2,2,1,2,1,1,2,..., and deleting the first term leaves a = A270648.

Mathematica

a = {2, 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: A275850 A112505 A104638 * A331034 A057155 A037812

Adjacent sequences: A270645 A270646 A270647 * A270649 A270650 A270651

Keyword

nonn,easy

Author

Clark Kimberling, Apr 07 2016

Status

approved