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 A004689 #19 Sep 08 2022 08:44:33
%S A004689 0,1,1,2,3,5,12,21,33,54,131,225,400,1025,1425,2454,4323,11221,15544,
%T A004689 31205,51153,122402,213555,340401,554400,1335201,2334001,4113202,
%U A004689 10451203,15004405,25500012,44504421,114404433
%N A004689 Fibonacci numbers written in base 6.
%H A004689 Vincenzo Librandi, <a href="/A004689/b004689.txt">Table of n, a(n) for n = 0..1000</a>
%t A004689 bf[n_,k_]:=Module[{s=ToString[BaseForm[n,k]]},ToExpression[StringDrop[s,{Part[StringPosition[s,"\n"],1,1],-1}]]] lst={};Do[f=bf[Fibonacci[n],6];AppendTo[lst,f],{n,0,4*4!}];lst (* _Vladimir Joseph Stephan Orlovsky_, Jun 17 2009 *)
%t A004689 FromDigits[IntegerDigits[#, 6]]& / @ Fibonacci[Range[0, 40]] (* _Vincenzo Librandi_, Jun 08 2013 *)
%o A004689 (PARI) vector(50, n, n--; fromdigits(digits(fibonacci(n), 6))) \\ _G. C. Greubel_, Oct 09 2018
%o A004689 (Magma) [Seqint(Intseq(Fibonacci(n),6)): n in [0..50]]; // _G. C. Greubel_, Oct 09 2018
%Y A004689 Cf. A000045 (Fibonacci), A007092 (numbers in base 6).
%K A004689 nonn,base,easy
%O A004689 0,4
%A A004689 _N. J. A. Sloane_