A023715 Numbers with exactly 2 2's in their base 4 expansion.

10, 26, 34, 38, 40, 41, 43, 46, 58, 74, 90, 98, 102, 104, 105, 107, 110, 122, 130, 134, 136, 137, 139, 142, 146, 150, 152, 153, 155, 158, 160, 161, 163, 164, 165, 167, 172, 173, 175, 178, 182, 184, 185, 187, 190, 202, 218, 226, 230, 232, 233, 235, 238, 250, 266

Offset

1,1

Links

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

Maple

q:= n-> numboccur(convert(n, base, 4), 2)=2:
select(q, [$1..350])[];  # Alois P. Heinz, Oct 26 2022

Mathematica

Select[ Range[ 240 ], (Count[ IntegerDigits[ #, 4 ], 2 ]==2)& ]

Prog

(Python)
def ok(n):
    mask, c = 3, 0
    for i in range(n.bit_length() >> 1):
        if (mask&n) >> (i << 1) == 2: c += 1
        mask <<= 2
    return c == 2
print([k for k in range(227) if ok(k)]) # Michael S. Branicky, Oct 26 2022

Crossrefs

Sequence in context: A337049 A067264 A043342 * A045143 A005278 A339977

Adjacent sequences: A023712 A023713 A023714 * A023716 A023717 A023718

Keyword

nonn,base,easy

Author

Olivier Gérard

Status

approved