A050428 Numbers for which in base 2 the least number of digits that can be removed to leave a base 2 palindromic number (beginning with 1) is 4.

16, 48, 80, 88, 104, 112, 144, 152, 156, 184, 200, 228, 232, 240, 272, 280, 284, 286, 296, 300, 302, 316, 328, 336, 344, 348, 376, 392, 420, 424, 432, 440, 452, 466, 468, 472, 482, 484, 488, 496, 528, 536, 540, 542, 543, 552, 556, 558, 559, 564, 566, 574, 606

Offset

1,1

Links

Table of n, a(n) for n=1..53.

Example

(64 base 2) = 10000 -> 1.

Prog

(Python)
from itertools import combinations
def ok(n):
    b = bin(n)[2:]
    for digs_to_remove in range(5):
        for skip in combinations(range(len(b)), digs_to_remove):
            newb = "".join(b[i] for i in range(len(b)) if i not in skip)
            if len(newb) > 0 and newb[0] == '1' and newb == newb[::-1]:
                return (digs_to_remove == 4)
    return False
print(list(filter(ok, range(607)))) # Michael S. Branicky, Aug 24 2021

Crossrefs

Cf. A050423, A050425, A050426, A050427, A050429.

Sequence in context: A336595 A069084 A084112 * A134605 A035008 A189972

Adjacent sequences: A050425 A050426 A050427 * A050429 A050430 A050431

Keyword

nonn,base

Author

Clark Kimberling

Status

approved