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 A031951 #23 Aug 10 2021 14:54:01
%S A031951 6,8,9,10,11,12,13,15,16,17,18,19,20,22,23,24,25,26,27,29,30,31,32,33,
%T A031951 34,36,37,42,44,45,46,47,49,50,55,57,61,64,67,71,72,74,79,80,84,85,87,
%U A031951 88,89,92,93,98,100,104,107,108,111,115,117
%N A031951 Numbers with exactly two distinct base-6 digits.
%H A031951 Robert Israel, <a href="/A031951/b031951.txt">Table of n, a(n) for n = 1..10000</a>
%H A031951 <a href="/index/Ar#6-automatic">Index entries for 6-automatic sequences</a>.
%p A031951 M:= 6: # get all terms < 6^M
%p A031951 sort([seq(seq(seq(seq(add(6^(m-j)*`if`(member(j,S2),d2,d1),j=1..m) ,
%p A031951 S2 = combinat:-powerset({$2..m}) minus {{}}),
%p A031951 d2 = {$0..5} minus {d1}), d1 = 1..5), m=2..M)]);# _Robert Israel_, Dec 03 2015
%t A031951 fQ[n_] := Length@ Union@ IntegerDigits[n, 6] == 2; Select[Range@117, fQ] (* _Robert G. Wilson v_, Dec 03 2015 *)
%Y A031951 Cf. A007092, A031948, A031949, A031950, A031952, A031953, A031954, A031955.
%K A031951 nonn,base,easy
%O A031951 1,1
%A A031951 _Clark Kimberling_