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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 (list; graph; refs; listen; history; text; internal format)
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..8.

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 * A111878 A133279 A192734

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

STATUS

approved

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Last modified August 5 01:32 EDT 2021. Contains 346456 sequences. (Running on oeis4.)