%I A006928 M0070
%S A006928 1,2,1,1,2,1,2,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,1,2,2,1,1,2,1,1,2,1,2,2,
               1,
%T A006928 2,2,1,1,2,1,2,2,1,2,1,1,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2,2,1,1,2,1,1,2,
               1,
%U A006928 2,2,1,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,1,2,2,
               1
%N A006928 a(n) = length of (n+1)st run, with initial terms 1, 2.
%D A006928 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A006928 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               KolakoskiSequence.html">Link to a section of The World of Mathematics.</
               a>
%F A006928 Essentially same as Kolakoski sequence A000002.
%e A006928 Start with [ 1,2 ]. a(1)=1, so the second run has length 1, so a(3) must 
               be 1. a(2)=2, so the third run has length 2, so a(4) must also be 
               1 and a(5) must be 2. a(3)=1, so the 4th run has length 1, so a(6) 
               must be 1; etc. (From Labos E.)
%o A006928 (PARI) a=[ 1,2 ]; for(n=2,80, for(i=1,a[ n ],a=concat(a,1+(n%2)))); a
%Y A006928 A006928(n)=A000002(n+1), n>1.
%Y A006928 Sequence in context: A078703 A090629 A086412 this_sequence A087890 A008676 
               A025893
%Y A006928 Adjacent sequences: A006925 A006926 A006927 this_sequence A006929 A006930 
               A006931
%K A006928 nonn,easy,nice
%O A006928 1,2
%A A006928 N. J. A. Sloane (njas(AT)research.att.com).