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Printjmc
number theory senior
Problem
Let be a natural number with exactly 2 positive prime divisors. If has 27 divisors, how many does have?
Solution
Let and be the prime divisors of , so we can write for positive integers and . This means , so . Since and are both greater than 1 and are divisors of 27, we know they are 3 and 9 (in no particular order). This means that and are 1 and 4 (in no particular order), so
Final answer
10