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 A031948 #16 Nov 25 2023 16:16:53 %S A031948 3,5,6,7,9,10,12,14,16,17,18,20,22,23,24,25,27,28,30,31,36,37,39,41, %T A031948 43,44,49,50,52,53,54,56,60,62,67,68,70,71,72,74,76,77,78,79,81,82,84, %U A031948 85,90,91,93,94,108,109,111,112,117,118,120,122 %N A031948 Numbers with exactly two distinct base-3 digits. %H A031948 Robert Israel, <a href="/A031948/b031948.txt">Table of n, a(n) for n = 1..10000</a> %p A031948 filter:= n -> nops(convert(convert(n,base,3),set))=2: %p A031948 select(filter, [$1..200]); # _Robert Israel_, Nov 29 2017 %t A031948 Select[Range[150],Length[Union[IntegerDigits[#,3]]]==2&] (* _Harvey P. Dale_, Nov 25 2023 *) %Y A031948 Cf. A007089. %K A031948 nonn,base %O A031948 1,1 %A A031948 _Clark Kimberling_