Browse · MathNet
PrintHrvatska 2011
Croatia 2011 number theory
Problem
In how many ways can the number be represented as a product of two fractions of the form , where is a positive integer? (Order of the factors is not important.)
Solution
Let and be positive integers such that . Then , i.e. .
From the last equation we find Since and are positive integers, it follows that is a positive divisor of . Each divisor of corresponds to exactly one pair . Since , the number of its divisors is . Finally, since the pairs and determine the same representation, the number of required representations is 16.
From the last equation we find Since and are positive integers, it follows that is a positive divisor of . Each divisor of corresponds to exactly one pair . Since , the number of its divisors is . Finally, since the pairs and determine the same representation, the number of required representations is 16.
Final answer
16
Techniques
Factorization techniquesτ (number of divisors)Techniques: modulo, size analysis, order analysis, inequalities