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 A305877 #42 Jun 26 2018 14:37:04
%S A305877 0,1,2,1,11,21,2,12,22,1,101,201,11,111,211,21,121,221,2,102,202,12,
%T A305877 112,212,22,122,222,1,1001,2001,101,1101,2101,201,1201,2201,11,1011,
%U A305877 2011,111,1111,2111,211,1211,2211,21,1021,2021,121,1121,2121,221,1221,2221,2
%N A305877 Numbers in base 3 reversed.
%H A305877 David F. Marrs, <a href="/A305877/b305877.txt">Table of n, a(n) for n = 0..10000</a>
%F A305877 a(n) = A004086(A007089(n)). - _Felix Fröhlich_, Jun 14 2018
%e A305877 11 is 102 in base 3, and reversing it gives 201 = a(11).
%p A305877 a:= n-> parse(cat(convert(n, base, 3)[])):
%p A305877 seq(a(n), n=0..75); # _Alois P. Heinz_, Jun 17 2018
%t A305877 Table[FromDigits@ Reverse@ IntegerDigits[n, 3], {n, 0, 54}] (* _Giovanni Resta_, Jun 13 2018 *)
%o A305877 (PARI) a(n) = fromdigits(Vecrev(digits(n, 3)), 10); \\ _Michel Marcus_, Jun 13 2018
%Y A305877 Cf. A004086 (in base 10), A007089, A030102 (when converted in base 10).
%K A305877 nonn,base,easy
%O A305877 0,3
%A A305877 _David F. Marrs_, Jun 13 2018