2020 AMC 12B Problem 24
Problem 24 of 25HarderNumber TheoryCounting & Probability
Let denote the number of ways of writing the positive integer as a product where the are integers strictly greater than and the order in which the factors are listed matters (that is, two representations that differ only in the order of the factors are counted as distinct). For example, the number can be written as and so What is
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Solution
The first factor can be any divisor after which the rest is an ordered factorization of So with
Computing over the divisors of
Finally
Thus, the correct answer is A.