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 A083570 #18 Sep 03 2025 13:10:32
%S A083570 0,0,1,1,2,2,1,0,2,0,0,1,1,2,2,1,0,2,0,0,1,1,2,2,1,0,2,0,0,1,1,2,2,1,
%T A083570 0,2,0,0,1,1,2,2,1,0,2,0,0,1,1,2,2,1,0,2,0,0,1,1,2,2,1,0,2,0,0,1,1,2,
%U A083570 2,1,0,2,0,0,1,1,2,2,1,0,2,0,0,1,1,2,2,1,0,2,0,0,1,1,2,2,1,0,2
%N A083570 A de Bruijn sequence of length 9 over {0, 1, 2}, repeated.
%C A083570 Each of the 9 pairs 00, 01, ..., 22 occurs exactly once in each period.
%H A083570 F. Mendivil, <a href="https://www.jstor.org/stable/3647906">Fractals, graphs and fields</a>, Amer. Math. Monthly, 110 (No. 6, 2003), 503-515.
%t A083570 PadRight[{},99,{0,0,1,1,2,2,1,0,2}] (* _Harvey P. Dale_, Nov 23 2011 *)
%K A083570 nonn,changed
%O A083570 0,5
%A A083570 _N. J. A. Sloane_, Jun 14 2003