Determine the total number of rational numbers of the form m/n, where m and n are positive integers such that:
(A) m/n lies in the interval (0, 1); and
(B) m and n are relatively prime; and
(C) mn = 25!
NOTE: "!" denotes the factorial symbol, where n! = 1*2*3*......*(n1)*n
I believe there are 256 such numbers.
There are 9 prime factors of 25! = 2^22*3^10*5^6*7^3*11^2*13*17*19*23
Each of these prime factors can only be a factor of m or n, so there are 2^9 ways to split m and n so they are relatively prime. In only half of these is m<n so the solution is 2^9/2=2^8=256
If we ignore condition (B) there are 2^(23*11*7*4*3*2*2*2*2)/2=2^340031 solutions.
If we ignore both (A) and (B) there are 2^340032 solutions

Posted by Jer
on 20061002 14:35:17 