A031948 Numbers with exactly two distinct base-3 digits.

3, 5, 6, 7, 9, 10, 12, 14, 16, 17, 18, 20, 22, 23, 24, 25, 27, 28, 30, 31, 36, 37, 39, 41, 43, 44, 49, 50, 52, 53, 54, 56, 60, 62, 67, 68, 70, 71, 72, 74, 76, 77, 78, 79, 81, 82, 84, 85, 90, 91, 93, 94, 108, 109, 111, 112, 117, 118, 120, 122

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• base

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A007089.

Programs

Maple

filter:= n -> nops(convert(convert(n,base,3),set))=2:
select(filter, [$1..200]); # Robert Israel, Nov 29 2017

Mathematica

Select[Range[150],Length[Union[IntegerDigits[#,3]]]==2&] (* Harvey P. Dale, Nov 25 2023 *)