Find all positive integers such that equation has exactly 2011 positive integer solutions with .
Solution
From the given equation, we have . Then, besides , for any equal to a proper divisor of , we will get a positive integer solution satisfying the required condition. Therefore, should have exactly 2010 proper divisors that are less than .
Suppose , where are prime numbers different from each other. Then the number of proper divisors of less than is
So . Since 4021 is prime, we get , and .
Therefore, , where is any prime number.
Want a route through all this instead of an archive? The track
puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.