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%I #3 Mar 30 2012 16:49:49
%S 2,1,2,2,1,1,2,1,1,2,2,1,2,2,1,2,1,1,2,1,1,2,2,1,2,1,1,2,1,2,2,1,1,2,
%T 1,1,2,2,1,2,2,1,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2,2,1,1,2,1,1,2,2,1,2,
%U 1,1,2,1,2,2,1,1,2,1,1,2,1,2,2,1,2,2,1,1,2,1,2,2,1,2,1,1,2,1,1,2,2,1,2,2,1
%N Given a sequence u consisting just of 1's and 2's, let f(u)(n) be the length of n-th run. Then we may define a sequence u = {a(n)} by a(n)=f^(n-1)(u)(1) (starting with n=1).
%C There are exactly three infinite sequences satisfying this relation, namely this sequence, A087889 and A087890.
%Y Cf. A000002, A087889, A087890.
%K easy,eigen,nonn
%O 1,1
%A Vincent Nesme (vincent.nesme(AT)ens-lyon.fr), Oct 13 2003
%E The description was not quite clear to me but I hope I have edited it correctly. - _N. J. A. Sloane_.
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