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A050427 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 3. 4
8, 24, 40, 44, 52, 56, 72, 76, 78, 92, 100, 114, 116, 120, 136, 140, 142, 143, 148, 150, 151, 158, 164, 168, 172, 174, 188, 196, 210, 212, 216, 220, 226, 233, 234, 236, 241, 242, 244, 248, 264, 268, 270, 271, 276, 278, 279, 282, 283, 287, 303, 308, 310, 318 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..54.

EXAMPLE

(72 base 2) = 1001000 -> 1001.

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[0] == '1' and newb == newb[::-1]:

                return (digs_to_remove == 3)

    return False

print(list(filter(ok, range(320)))) # Michael S. Branicky, Aug 24 2021

CROSSREFS

Cf. A050425, A050426, A050428, A050429.

Sequence in context: A134223 A304475 A316300 * A329549 A031046 A173080

Adjacent sequences:  A050424 A050425 A050426 * A050428 A050429 A050430

KEYWORD

nonn,base

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified September 26 20:34 EDT 2021. Contains 347672 sequences. (Running on oeis4.)