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 A181986 #12 Mar 15 2020 12:43:49
%S A181986 102,120,201,210,100122,100212,100221,101022,101202,101220,102012,
%T A181986 102021,102102,102120,102201,102210,110022,110202,110220,112002,
%U A181986 112020,112200,120012,120021,120102,120120,120201,120210,121002,121020,121200,122001,122010,122100
%N A181986 Digitally balanced numbers: ternary numbers which have the same number of 0's as 1's as 2's.
%C A181986 This is to A071925 as base 3 A007089 is to base 2 A007088. A049354 digitally balanced numbers in base 3: equal numbers of 0's, 1's, 2's, beginning 11, 15, 19, 21, 260, ... is the same sequence, but expressed in base 10. The terms of this sequence are represented directly in base 3.
%H A181986 Alois P. Heinz, <a href="/A181986/b181986.txt">Table of n, a(n) for n = 1..2000</a>
%e A181986 100122 is an element because it contains two each of "0" and "1" and "2".
%t A181986 Select[FromDigits/@Flatten[Permutations/@Table[PadRight[{},3n,{0,1,2}],{n,2}],1],Mod[IntegerLength[#],3]==0&]//Sort (* _Harvey P. Dale_, Mar 15 2020 *)
%Y A181986 Cf. A007089, A031443, A049354, A071925.
%K A181986 nonn,base
%O A181986 1,1
%A A181986 _Jonathan Vos Post_, Apr 04 2012
%E A181986 More terms from _Alois P. Heinz_, Apr 05 2012