A023719 - OEIS

%I #20 Aug 11 2024 15:18:24

%S 15,31,47,51,55,59,60,61,62,79,95,111,115,119,123,124,125,126,143,159,

%T 175,179,183,187,188,189,190,195,199,203,204,205,206,211,215,219,220,

%U 221,222,227,231,235,236,237,238,240,241,242,244,245,246,248,249,250

%N Numbers with exactly two 3's in their base 4 expansion.

%H Seiichi Manyama, <a href="/A023719/b023719.txt">Table of n, a(n) for n = 1..10000</a>

%e 62 in base 4 is 332. As that has precisely two 3's, 62 is in the sequence.

%e 63 in base 4 is 333. As that has one more 3 than specified, 63 is not in the sequence.

%p select(k-> numboccur(3, convert(k, base, 4))=2, [$0..500])[];  # _Alois P. Heinz_, Feb 22 2019

%t Select[Range[260], Count[IntegerDigits[#, 4], 3] == 2 &]

%t Select[Range[300],DigitCount[#,4,3]==2&] (* _Harvey P. Dale_, Aug 11 2024 *)

%K nonn,base,easy

%O 1,1

%A _Olivier Gérard_