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 A043530 #25 Apr 24 2021 21:28:34
%S A043530 1,1,2,1,2,2,2,1,2,2,3,2,1,2,3,2,2,2,3,2,3,2,2,2,2,1,2,2,3,2,2,3,3,3,
%T A043530 3,2,2,3,2,1,2,3,2,2,3,3,3,3,2,2,3,2,2,2,3,2,3,3,3,2,3,2,3,3,3,3,2,2,
%U A043530 3,2,2,2,3,2,3,2,2,2,2,1,2,2,3,2,2,3,3,3,3,2
%N A043530 Number of distinct base-3 digits of n.
%C A043530 a(A031944(n)) = 3; a(A154314(n)) < 3. - _Reinhard Zumkeller_, Jan 07 2009
%C A043530 Image, under the coding sending i -> 1+floor(i/3), of the fixed point, starting with 0, of the morphism 0 -> 012, 1 -> 314, 2 -> 542, 3 -> 336, 4 -> 644, 5 -> 565, 6 -> 666. - _Jeffrey Shallit_, May 15 2016
%H A043530 Antti Karttunen, <a href="/A043530/b043530.txt">Table of n, a(n) for n = 1..19683</a>
%t A043530 Table[Length[Union[IntegerDigits[n,3]]],{n,90}] (* _Harvey P. Dale_, May 13 2020 *)
%o A043530 (PARI) a(n) = #vecsort(digits(n,3),,8); \\ _Michel Marcus_, May 16 2016
%Y A043530 Cf. A007089, A031944, A037897, A154314.
%K A043530 nonn,base
%O A043530 1,3
%A A043530 _Clark Kimberling_