A269349 Kolakoski-(1,7) sequence: a(n) is length of n-th run.

1, 7, 7, 7, 7, 7, 7, 7, 1, 1, 1, 1, 1, 1, 1, 7, 7, 7, 7, 7, 7, 7, 1, 1, 1, 1, 1, 1, 1, 7, 7, 7, 7, 7, 7, 7, 1, 1, 1, 1, 1, 1, 1, 7, 7, 7, 7, 7, 7, 7, 1, 7, 1, 7, 1, 7, 1, 7, 7, 7, 7, 7, 7, 7, 1, 1, 1, 1, 1, 1, 1, 7, 7, 7, 7, 7, 7, 7, 1, 1, 1, 1, 1, 1, 1, 7, 7

Offset: 1

Author

Vincenzo Librandi, Feb 26 2016

Keywords

• nonn
• easy

Comments

17, 1777, 1777777711111117777777 are primes.

Links

• Vincenzo Librandi, 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.

Crossrefs

Cf. similar sequences listed in A269268.

Programs

Mathematica

seed = {1, 7}; 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