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Kolakoski-(1,7) sequence: a(n) is length of n-th run.
2

%I #14 Mar 03 2016 03:41:42

%S 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,

%T 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,

%U 1,1,1,7,7,7,7,7,7,7,1,1,1,1,1,1,1,7,7

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

%C 17, 1777, 1777777711111117777777 are primes.

%H Vincenzo Librandi, <a href="/A269349/b269349.txt">Table of n, a(n) for n = 1..10000</a>

%H Michael Baake and Bernd Sing, <a href="http://arXiv.org/abs/math.MG/0206098">Kolakoski-(3,1) is a (deformed) model set</a>, arXiv:math/0206098 [math.MG], 2002-2003.

%t 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

%Y Cf. similar sequences listed in A269268.

%K nonn,easy

%O 1,2

%A _Vincenzo Librandi_, Feb 26 2016