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 A256303 #5 Jun 17 2022 18:06:21
%S A256303 1,2,0,21,22,20,1,2,0,211,212,210,221,222,220,201,202,200,11,12,10,21,
%T A256303 22,20,1,2,0,2111,2112,2110,2121,2122,2120,2101,2102,2100,2211,2212,
%U A256303 2210,2221,2222,2220,2201,2202,2200,2011,2012,2010,2021,2022,2020,2001
%N A256303 Apply the transformation 0 -> 1 -> 2 -> 0 to the digits of n written in base 3; do not convert back to base 10.
%C A256303 Base 3 variant of A256078 (base 2) and A048379 (base 10). See A256304 - A256308 for bases 4 through 8, A256289 for base 9, and A256293 for the variant where the result is converted back to base 10.
%e A256303 a(3) = 21 because 3 = "10" (in base 3) becomes "21".
%e A256303 a(8) = 0 because 8 = "22" (in base 3) becomes "00".
%t A256303 Table[FromDigits[IntegerDigits[n,3]/.{0->1,1->2,2->0}],{n,0,60}] (* _Harvey P. Dale_, Jun 17 2022 *)
%o A256303 (PARI) A256303(n,b=3)=!n+eval(Strchr(apply(d->(d+1)%b+48, digits(n,b))))
%K A256303 nonn,base,easy
%O A256303 0,2
%A A256303 _M. F. Hasler_, Mar 22 2015