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

15, 31, 47, 51, 55, 59, 60, 61, 62, 79, 95, 111, 115, 119, 123, 124, 125, 126, 143, 159, 175, 179, 183, 187, 188, 189, 190, 195, 199, 203, 204, 205, 206, 211, 215, 219, 220, 221, 222, 227, 231, 235, 236, 237, 238, 240, 241, 242, 244, 245, 246, 248, 249, 250

Offset

1,1

Links

Seiichi Manyama, Table of n, a(n) for n = 1..10000

Example

62 in base 4 is 332. As that has precisely two 3's, 62 is in the sequence.
63 in base 4 is 333. As that has one more 3 than specified, 63 is not in the sequence.

Maple

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

Mathematica

Select[Range[260], Count[IntegerDigits[#, 4], 3] == 2 &]
Select[Range[300], DigitCount[#, 4, 3]==2&] (* Harvey P. Dale, Aug 11 2024 *)

Crossrefs

Sequence in context: A041440 A042017 A043346 * A031467 A045063 A044076

Adjacent sequences: A023716 A023717 A023718 * A023720 A023721 A023722

Keyword

nonn,base,easy

Author

Olivier Gérard

Status

approved