2019 AMC 12B Problem 14
Problem 14 of 25IntermediateNumber TheoryCounting & Probability
Let be the set of all positive integer divisors of How many numbers are the product of two distinct elements of
Answer choices
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Solution
Since every divisor is with A product of two divisors is with and every such pair is attainable, giving values.
We need two distinct divisors. A value is forced to be a divisor times itself only when both and have a unique split, which happens exactly when Those corner values () cannot use two distinct divisors.
The count is
Thus, C is the correct answer.