%I A060146
%S A060146 1,1,7,21,190,1007,6972,111554
%N A060146 Take the first 2n integers and using each integer once and only once 
               as either a numerator or a denominator, construct n fractions whose 
               sum is an integer; a(n) = number of unique solutions for n.
%C A060146 The old entry with this sequence number was a duplicate of A048298.
%o A060146 (PARI) /* from Max Alekseyev */
%o A060146 { npairs(n) = loca(r,q,z); r=0;
%o A060146 forvec(p=vector(n,i,[1,2*n]),
%o A060146 q = eval( setminus( Set(vector(2*n,i,i)), Set(p) ) );
%o A060146 for(j=1,n!,
%o A060146 z=numtoperm(n,j);
%o A060146 if(type( sum(j=1,#p,p[j]/q[z[j]]) )=="t_INT",r++); );, 2); r }
%Y A060146 Sequence in context: A028248 A032032 A084711 this_sequence A111878 A133279 
               A082826
%Y A060146 Adjacent sequences: A060143 A060144 A060145 this_sequence A060147 A060148 
               A060149
%K A060146 nonn
%O A060146 1,3
%A A060146 Jack Brennen (jb(AT)brennen.net), May 13 2008
%E A060146 a(6)-a(8) from Max Alekseyev (maxale(AT)gmail.com), May 14 2008
%E A060146 Edited by Charles R Greathouse IV (charles.greathouse(AT)case.edu), Oct 
               28 2009