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 A023719 Numbers with exactly two 3's in base 4 expansion. 1

%I

%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 base 4 expansion.

%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 &]

%K nonn,base,easy

%O 1,1

%A _Olivier Gérard_

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Last modified December 4 19:40 EST 2021. Contains 349526 sequences. (Running on oeis4.)