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imc

number theory intermediate

Problem

How many positive integer divisors of are perfect squares or perfect cubes (or both)?
(A)
(B)
(C)
(D)
Solution
Prime factorizing , we get . A perfect square must have even powers of its prime factors, so our possible choices for our exponents to get perfect square are for both and . This yields perfect squares. Perfect cubes must have multiples of for each of their prime factors' exponents, so we have either , or for both and , which yields perfect cubes, for a total of . Subtracting the overcounted powers of ( , , , and ), we get .
Final answer
C