A089310 Write n in binary; a(n) = number of 1's in second block of 1's from right.

0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 2, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 2, 2, 2, 0, 3, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 0, 2, 2, 2, 2, 1, 2, 2, 0, 3, 3, 3, 0, 4, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 3, 1, 1, 0, 2, 2, 2

Offset: 0

Author

N. J. A. Sloane, Dec 22 2003

Keywords

• nonn
• base

Examples

			13 = 1101 so a(13) = 2.
		

Links

• Robert Israel, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A089309, A089311, A089312, A089313.

Programs

Maple

f:= proc(n) local t,q,r;
  r:= 0: t:= n;
  while t::even do t:= t/2 od;
  while t::odd do t:= (t-1)/2 od;
  if t = 0 then return 0 fi;
  while t::even do t:= t/2 od;
  while t::odd do r:= r+1; t:= (t-1)/2 od;
  r
end proc:
f(0):= 0:
map(f, [$0..100]); # Robert Israel, Aug 03 2025

PARI

a(n)=my(b, c, s); if(n==0,return(0)); b=binary(n); c=length(b); while(!b[c], c=c-1); while(c>0&&b[c], c=c-1); if(c<=0, 0, while(!b[c], c=c-1); s=0; while(c>0&&b[c], c=c-1;s=s+1);s) /* Ralf Stephan, Feb 01 2004 */

Extensions

More terms from Ralf Stephan, Feb 01 2004