cp's OEIS Frontend

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 distinct solutions for n.

%I A060146 #18 Oct 29 2022 04:34:09
%S A060146 1,1,7,21,190,1007,6972,111554,1040635
%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 distinct solutions for n.
%C A060146 The old entry with this sequence number was a duplicate of A048298.
%o A060146 (PARI) { 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 }
%o A060146 /* _Max Alekseyev_, May 14 2008 */
%K A060146 nonn
%O A060146 1,3
%A A060146 _Jack Brennen_, May 13 2008
%E A060146 a(6)-a(8) from _Max Alekseyev_, May 14 2008
%E A060146 Edited by _Charles R Greathouse IV_, Oct 28 2009
%E A060146 a(9) from _Sean A. Irvine_, Oct 29 2022