%I A157001
%S A157001 0,1,2,5,7,11,14,21,25,32,37,47,53,63,70,85,93,106,115,132,142,158,169,
%T A157001 191,203,222,235,259,273,295,310,341,357,382,399,430,448,476,495,532,
%U A157001 552,583,604,642,664,698,721,767,791,828,853,898,924,964,991,1043,1071
%N A157001 Fractions x/y, with 1<=x,y<=n, that reduce to (odd)/(even).
%C A157001 Equivalently, a(n) is the number of fractions x/y, with 1<=x,y<=n, that 
               reduce to (even)/(odd).
%Y A157001 a(n)=(n^2-A135013)/2
%Y A157001 Sequence in context: A099835 A133436 A001225 this_sequence A134640 A032616 
               A006066
%Y A157001 Adjacent sequences: A156998 A156999 A157000 this_sequence A157002 A157003 
               A157004
%K A157001 nonn
%O A157001 1,3
%A A157001 Adam McDougall (mcdougall.adam(AT)gmail.com), Feb 20 2009