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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.
0
1, 1, 7, 21, 190, 1007, 6972, 111554, 1040635
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OFFSET
1,3
COMMENTS
The old entry with this sequence number was a duplicate of
A048298
.
LINKS
Table of n, a(n) for n=1..9.
PROG
(PARI) { npairs(n) = loca(r, q, z); r=0;
forvec(p=vector(n, i, [1, 2*n]),
q = eval( setminus( Set(vector(2*n, i, i)), Set(p) ) );
for(j=1, n!,
z=numtoperm(n, j);
if(type( sum(j=1, #p, p[j]/q[z[j]]) )=="t_INT", r++); ); , 2); r }
/*
Max Alekseyev
, May 14 2008 */
CROSSREFS
Sequence in context:
A032032
A084711
A183938
*
A357673
A111878
A133279
Adjacent sequences:
A060143
A060144
A060145
*
A060147
A060148
A060149
KEYWORD
nonn
AUTHOR
Jack Brennen
, May 13 2008
EXTENSIONS
a(6)a(8) from
Max Alekseyev
, May 14 2008
Edited by
Charles R Greathouse IV
, Oct 28 2009
a(9) from
Sean A. Irvine
, Oct 29 2022
STATUS
approved
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Last modified September 30 05:24 EDT 2023. Contains 365781 sequences. (Running on oeis4.)