A246591 Smallest number that can be obtained by swapping 2 bits in the binary expansion of n.

0, 1, 1, 3, 1, 3, 3, 7, 1, 3, 3, 7, 5, 7, 7, 15, 1, 3, 3, 7, 5, 7, 7, 15, 9, 11, 11, 15, 13, 15, 15, 31, 1, 3, 3, 7, 5, 7, 7, 15, 9, 11, 11, 15, 13, 15, 15, 31, 17, 19, 19, 23, 21, 23, 23, 31, 25, 27, 27, 31, 29, 31, 31, 63, 1, 3, 3, 7, 5, 7, 7, 15, 9, 11, 11

Offset

0,4

Comments

Swap the first 1 with the last 0 in the binary expansion of n.

Links

Alois P. Heinz, Table of n, a(n) for n = 0..8190

Example

If n = 12 = 1100_2 then a(12) = 0101_2 = 5.

Prog

(Python)
from itertools import combinations
def A246591(n):
    if n <= 1:
        return n
    else:
        s = bin(n)[2:]
        l = len(s)
        y = 2**l-1
        for i in combinations(range(l), 2):
            s2 = int(s[:i[0]]+s[i[1]]+s[i[0]+1:i[1]]+s[i[0]]+s[i[1]+1:], 2)
            if s2 < y:
                y = s2
        return y
# Chai Wah Wu, Sep 05 2014
(Python)
def A246591(n):
    s = bin(n)[2:]
    s2 = s.rstrip('1')
    return(int(s2[1:-1]+'1'+s[len(s2):], 2) if (len(s2) > 0 and n > 1) else n)
# Chai Wah Wu, Sep 08 2014

Crossrefs

Cf. A241816, A246592, A246593, A246594.

Sequence in context: A061892 A382755 A038573 * A173465 A151837 A356354

Adjacent sequences: A246588 A246589 A246590 * A246592 A246593 A246594

Keyword

nonn,base

Author

N. J. A. Sloane, Sep 03 2014

Extensions

More terms from Alois P. Heinz, Sep 03 2014

Status

approved