A246594 - OEIS

%I #25 Sep 07 2014 08:05:38

%S 0,1,2,3,4,6,6,7,8,10,12,13,12,14,14,15,16,18,20,21,24,25,26,27,24,26,

%T 28,29,28,30,30,31,32,34,36,37,40,41,42,43,48,49,50,51,52,53,54,55,48,

%U 50,52,53,56,57,58,59,56,58,60,61,60,62,62,63,64,66,68

%N a(n)=n for n <= 2; for n >= 3, a(n) = largest number that can be obtained by swapping two adjacent bits in the binary expansion of n.

%C In both this sequence and A246593 you are not allowed to touch any of the invisible 0's before the leading 1.

%C Scanning from the left, find first occurrence of '01' in binary expansion and replace with '10' and return decimal representation or return n if no such swap exists. - _Chai Wah Wu_, Sep 06 2014

%H Alois P. Heinz, <a href="/A246594/b246594.txt">Table of n, a(n) for n = 0..8192</a>

%e If n = 17 = 10001_2 then a(17) = 10010_2 = 18.

%o (Python)

%o def A246594(n):

%o ....s = bin(n)[2:]

%o ....for i in range(len(s)-1):

%o ........if s[i:i+2] == '01':

%o ............return int(s[:i]+'10'+s[i+2:],2)

%o ....else:

%o ........return n # _Chai Wah Wu_, Sep 06 2014

%Y Cf. A241816, A246591, A246592, A246593.

%K nonn,base

%O 0,3

%A _N. J. A. Sloane_, Sep 03 2014

%E Corrected definition and more terms from _Alois P. Heinz_, Sep 04 2014

%E Corrected typo in definition - _Chai Wah Wu_, Sep 06 2014