A071907 Kolakoski-(1,4) sequence: a(n) is length of n-th run.

1, 4, 4, 4, 4, 1, 1, 1, 1, 4, 4, 4, 4, 1, 1, 1, 1, 4, 1, 4, 1, 4, 4, 4, 4, 1, 1, 1, 1, 4, 4, 4, 4, 1, 1, 1, 1, 4, 1, 4, 1, 4, 4, 4, 4, 1, 4, 4, 4, 4, 1, 4, 4, 4, 4, 1, 1, 1, 1, 4, 4, 4, 4, 1, 1, 1, 1, 4, 1, 4, 1, 4, 4, 4, 4, 1, 1, 1, 1, 4, 4, 4, 4, 1, 1, 1, 1, 4, 1, 4, 1, 4, 4, 4, 4, 1, 4, 4, 4, 4, 1, 4, 4, 4, 4

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Comments

1444411, 14444111144441111414144441111 are primes. - Vincenzo Librandi, Mar 02 2016

Links

• Ivan Neretin, Table of n, a(n) for n = 1..10000
• Michael Baake and Bernd Sing, Kolakoski-(3,1) is a (deformed) model set, arXiv:math/0206098 [math.MG], 2002-2003.
• Rémy Sigrist, Scatterplot of twice the number of ones among the first n terms of the sequence minus n for n = 1..1000000

Crossrefs

Cf. A000002, A071820, A064353, A071928, A071942.

Programs

Mathematica

seed = {1, 4}; w = {}; i = 1; Do[w = Join[w,Array[seed[[Mod[i - 1, Length[seed]] + 1]] &, If[i > Length[w], seed, w][[i]]]]; i++, {n, 42}]; w (* Ivan Neretin, Apr 02 2015 *)