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a)What is the smallest positive integer that has exactly 20 positive divisors?

 

b)What is the smallest positive integer that has exactly 6 perfect square divisors?

 Mar 24, 2019
 #1
avatar+4779 
+4

\(20 = 2^2 5 \text{ so we'll want to use prime factors }\\ 2^4 \cdot 3^1 \cdot 5^1 = 240\\ \text{This has }(4+1)(1+1)(1+1)=20 \text{ divisors}\)

 

I'm pretty sure for (2) we just find the smallest positive integer with 6 divisors and square it.

Proceeding as above

 

\(6=2\cdot 3 \text{ so choose}\\ (2^2\cdot 3)^2 = 144\)

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 Mar 24, 2019
 #2
avatar+290 
+2

Thank You!

Badada  Mar 24, 2019
 #3
avatar+533 
+1

a)

20 has factors of 1, 2, 4, 5, 10, and 20. So, to make the number as small as possible, we want to use 5 * 2 * 2. We will pair the largest exponents with the smaller primes to get 2^(5-1) * 3 * 5 = 240.

 

b)

It has 6 perfect square divisors, so we need the smallest number with 6 divisors then square that to get the answer. That is (by counting), 12. So, our answer is 12^2 = 144.

 Mar 24, 2019

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