The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 (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..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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 30 05:24 EDT 2023. Contains 365781 sequences. (Running on oeis4.)