For positive integer , let be the number of ways of factoring into product of positive integers greater than (The order of factors are not countered, for example , as can be factored in these ways: .
Prove: If is a positive integer greater than , is a prime factor of , then
Problem 1705
Official solution
For a positive integer , let represent the number of ways to factor into a product of positive integers greater than 1. For example, because 12 can be factored in these 4 ways: , , , and .
We aim to prove that if is a positive integer greater than 1 and is a prime factor of , then .
We proceed by using strong induction. The base case is clear.
Let be the largest prime divisor of . We need to show that .
Consider where each . Suppose one of the factors . Then must divide , implying that:
By the inductive hypothesis, for any , we have , where is the largest prime factor of and is the Euler's totient function.
Thus, we can write:
Therefore, we have shown that as required.
The answer is: \boxed{\frac{n}{p}}.