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 A317199 #9 Aug 05 2018 13:50:25
%S A317199 12,213,3121,121312,2131211213
%N A317199 Bo Tan et al.'s string E_n, defined by A_n = A103269(n) = D_{n-1}E_n = A317197(n-1)E_n for n >= 2, with E_1 = 12.
%C A317199 See A317200 for length of E_n.
%H A317199 Bo Tan and Zhi-Ying Wen, <a href="http://dx.doi.org/10.1016/j.ejc.2006.07.007">Some properties of the Tribonacci sequence</a>, European Journal of Combinatorics, 28 (2007) 1703-1719. See E_n, p. 1706.
%e A317199 A_4 = 1213121121312, D_3 = 1213121, so E_4 = 121312.
%Y A317199 Cf. A103269, A317197, A317200.
%Y A317199 See A317201 for the reversals of these words.
%K A317199 nonn,more
%O A317199 1,1
%A A317199 _N. J. A. Sloane_, Aug 05 2018