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 A291797 #5 Sep 04 2017 21:50:34
%S A291797 111,211,111111,111211,211111,211211,111111111,111111211,111211111,
%T A291797 111211211,211111111,211111211,211211111,211211211,111111111111,
%U A291797 111111111111,111111111211,111111211111,111111211211,111211111111,111211111211
%N A291797 Over the alphabet {1,2} let A=111, B=211; sequence lists words A, B, AA, AB, BA, BB, AAA, AAB, ...
%H A291797 Peter R. J. Asveld, <a href="http://doc.utwente.nl/66184/1/1988m20.pdf">On a Post's System of Tag</a>. Bulletin of the EATCS 36 (1988), 96-102. See Table 3.
%K A291797 nonn
%O A291797 1,1
%A A291797 _N. J. A. Sloane_, Sep 04 2017