%I #4 Mar 30 2012 18:50:54

%S 1,3,7,11,19,23,35,41,53,59,67,77,101,109,131,161,179,197,205,227,247,

%T 289,317,333,381,407,431,445,473,495,555,575,629,657,693,729,751,801,

%U 835,877,957,975,1059,1097,1147,1209,1235,1283,1335,1367,1397,1499,1539

%N Number of distinct rational numbers that can be written as fractions of the first n composite numbers.

%C a(n) = 2*A117992(n) + 1.

%e n=3, the first 3 composite numbers are 4,6 and 8:

%e a(3) = #{4/4, 4/6, 4/8, 6/4, 6/6, 6/8, 8/4, 8/6, 8/8} =

%e = #{1/2, 2/3, 3/4, 1/1, 4/3, 3/2, 2/1} = 7.

%Y Cf. A018805.

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, Apr 08 2006