This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A133235 #8 May 25 2013 23:55:31 %S A133235 22,2222,22211222,22211222211222,222112222112211222211222, %T A133235 2221122221122112222112222112211222211222, %U A133235 222112222112211222211222211221122221122112222112222112211222211222 %N A133235 Numerical encoding of a series of binary words generated by a recurrence - see comments. %C A133235 The sequence of words is bb, bbbb, bbbaabbb, bbbaabbbbaabbb, bbbaabbbbaabbaabbbbaabbb, ... given by the rule that the n-th word consists of the (n-1)st word, followed by the inverse of the (n-3)rd word, followed by the (n-1)st word. %C A133235 Here a (or 1) and 2 (or b) represent the respective matrices %C A133235 [1 1] [2 1] %C A133235 [1 0] [1 0] %C A133235 arising in the study of Markov numbers (A002559) - see link. %C A133235 Question: Can this substitution-deletion system be described by a simple morphism of the type shown in A008352? %H A133235 Tom Ace, <a href="http://www.minortriad.com/mmat.html">Calculating Markoff numbers with matrices</a> %e A133235 a(4) = bbbaabbbbaabbaabbbbaabbb, a(2) = bbbaabbb, so a(5) = bbbaabbbbaabbaabbbbaabbb (bbbaabbb)^(-1) bbbaabbbbaabbaabbbbaabbb = bbbaabbbbaabbaabbbbaabbbbaabbaabbbbaabbb %Y A133235 Cf. A002559, A008352, A003849. %K A133235 nonn %O A133235 0,1 %A A133235 _N. J. A. Sloane_, Oct 14 2007, based on an email message from _James Propp_, Jan 28 2005