A050422 Numbers for which in base 2 the least number of digits that can be removed to leave a palindrome (possibly beginning with 0) is 3.

52, 56, 88, 104, 112, 114, 116, 120, 142, 143, 150, 151, 168, 176, 184, 196, 200, 208, 212, 216, 220, 224, 226, 228, 233, 234, 236, 241, 242, 244, 248, 268, 270, 271, 278, 279, 282, 283, 286, 287, 302, 303, 304, 332, 334, 335, 336, 344, 352, 356, 360, 376, 388

Offset

1,1

Links

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

Example

(88 base 2) = 1011000 -> 0000.

Prog

(Python)
from itertools import combinations
def ok(n):
    b = bin(n)[2:]
    for digs_to_remove in range(4):
        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 == newb[::-1]:
                return (digs_to_remove == 3)
    return False
print(list(filter(ok, range(390)))) # Michael S. Branicky, Aug 24 2021

Crossrefs

Cf. A050427, A050420, A050421, A050423, A050424.

Sequence in context: A295156 A181461 A346455 * A350232 A226753 A260992

Adjacent sequences: A050419 A050420 A050421 * A050423 A050424 A050425

Keyword

nonn,base

Author

Clark Kimberling

Status

approved