%I #7 Jun 07 2013 13:35:28
%S 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,
%T 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,
%U 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
%N Write n in binary; a(n) = number of 1's in second block of 1's from right.
%e 13 = 1101 so a(13) = 2.
%o (PARI) a(n)=local(b,c,s):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_ */
%Y Cf. A089309-A089313.
%K nonn,base
%O 0,14
%A _N. J. A. Sloane_, Dec 22 2003
%E More terms from _Ralf Stephan_, Feb 01 2004