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 A004686 #16 Sep 08 2022 08:44:33
%S A004686 0,1,1,2,10,12,22,111,210,1021,2001,10022,12100,22122,111222,211121,
%T A004686 1100120,2012011,10112201,12201212,100021120,120000102,220021222,
%U A004686 1110022101,2100121100,10210220201,20011112001
%N A004686 Fibonacci numbers written in base 3.
%H A004686 Vincenzo Librandi, <a href="/A004686/b004686.txt">Table of n, a(n) for n = 0..1000</a>
%t A004686 Table[BaseForm[Fibonacci[n],3],{n,1,20,1}] (* _Vladimir Joseph Stephan Orlovsky_, Jul 23 2008 *)
%t A004686 FromDigits[IntegerDigits[#, 3]]& / @Fibonacci[Range[0, 50]] (* _Vincenzo Librandi_, Jun 07 2013 *)
%o A004686 (PARI) vector(50, n, n--; fromdigits(digits(fibonacci(n), 3))) \\ _G. C. Greubel_, Oct 09 2018
%o A004686 (Magma) [Seqint(Intseq(Fibonacci(n),3)): n in [0..50]]; // _G. C. Greubel_, Oct 09 2018
%Y A004686 Cf. A000045 (Fibonacci), A007089 (numbers in base 3).
%K A004686 nonn,base,easy
%O A004686 0,4
%A A004686 _N. J. A. Sloane_