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A246593
a(n)=n for n <= 2; for n >= 3, a(n) = largest number that can be obtained by swapping two bits in the binary expansion of n.
6
0, 1, 2, 3, 4, 6, 6, 7, 8, 12, 12, 14, 12, 14, 14, 15, 16, 24, 24, 26, 24, 28, 28, 30, 24, 28, 28, 30, 28, 30, 30, 31, 32, 48, 48, 50, 48, 52, 52, 54, 48, 56, 56, 58, 56, 60, 60, 62, 48, 56, 56, 58, 56, 60, 60, 62, 56, 60, 60, 62, 60, 62, 62, 63, 64, 96, 96
OFFSET
0,3
COMMENTS
In both this sequence and A246594 you are not allowed to touch any of the invisible 0's before the leading 1.
Swap first 0 with last 1 in the binary expansion of n or return n if no such swap is possible. - Chai Wah Wu, Sep 08 2014
LINKS
EXAMPLE
If n = 17 = 10001_2 then a(17) = 11000_2 = 24.
PROG
(Python)
from itertools import combinations
def A246593(n):
....if n <= 1:
........return n
....else:
........s, y = bin(n)[2:], n
........for i in combinations(range(len(s)), 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)
# implement algorithm in comment
def A246593(n):
....s = bin(n)[2:]
....s2 = s.rstrip('0')
....s3 = s2.lstrip('1')
....return(int(s2[:-len(s3)]+'1'+s3[1:-1]+'0'+s[len(s2):], 2) if (len(s3) > 0 and n > 1) else n)
# Chai Wah Wu, Sep 08 2014
CROSSREFS
KEYWORD
nonn,base
AUTHOR
N. J. A. Sloane, Sep 03 2014
EXTENSIONS
Corrected definition and more terms from Alois P. Heinz, Sep 04 2014
STATUS
approved