%I A078880
%S A078880 2,2,1,1,2,1,2,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,1,2,2,1,1,2,1,1,2,1,2,2,
%T A078880 1,2,2,1,1,2,1,2,2,1,2,1,1,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2,2,1,1,2,1,1,
%U A078880 2,1,2,2,1,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,1
%N A078880 The sequence starting with 2 that equals its own run length sequence.
%C A078880 It is an unsolved problem to show that the density of 1's is equal to 
               1/2.
%D A078880 M. S. Keane, Ergodic theory and subshifts of finite type, Chap. 2 of 
               T. Bedford et al., eds., Ergodic Theory, Symbolic Dynamics and Hyperbolic 
               Spaces, Oxford, 1991, esp. p. 50.
%F A078880 a(n) = k(n+1), where k=A000002, the Kolakoski sequence.
%e A078880 Start with 2, which generates 22 (so that the first run length is 2); 
               then 22 generates 2211 (so that the first two run lengths are 2 and 
               2); then 2211 generates 221121 and so on.
%Y A078880 See A000002, the official version of this sequence, for formulae, references, 
               links, etc.
%Y A078880 Sequence in context: A167677 A074293 A013949 this_sequence A000002 A074295 
               A116514
%Y A078880 Adjacent sequences: A078877 A078878 A078879 this_sequence A078881 A078882 
               A078883
%K A078880 nonn
%O A078880 1,1
%A A078880 Clark Kimberling (ck6(AT)evansville.edu), Dec 11 2002