A031949 - OEIS

%I #15 Aug 10 2021 18:46:40

%S 4,6,7,8,9,11,12,13,14,16,17,20,22,23,25,26,29,31,32,34,37,38,40,41,

%T 43,46,47,48,51,53,55,58,59,60,61,62,64,65,68,69,80,81,84,86,87,89,90,

%U 93,95,101,102,105,106,117,119,125,127,128,130

%N Numbers with exactly two distinct base-4 digits.

%t db4Q[n_]:=Count[DigitCount[n,4],_?(#>0&)]==2; Select[Range[200],db4Q] (* _Harvey P. Dale_, Jan 13 2019 *)

%Y Cf. A007090.

%K nonn,base

%O 1,1

%A _Clark Kimberling_