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# if sqrt(x) is a positive integer, is sqrt(x) a prime number?

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if sqrt(x) is a positive integer, is sqrt(x) a prime number? [#permalink]  31 Aug 2006, 14:34
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if sqrt(x) is a positive integer, is sqrt(x) a prime number?

1) x is divisible by exactly 3 positive integers
2) all positive factors of x are odd
Intern
Joined: 24 Aug 2006
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how do you know it's A?
Intern
Joined: 18 Aug 2006
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I'm not sure it's A.

Take a neat square number like 121 as an example.

121 factors to 11 * 11 * 1 so in this case it has 3 factors, 11^2 and itself.

But take 15. Factors to 5 * 3 * 1 but sqrt(15) is not prime as far as I know .

Am I missing something?
Intern
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Never mind. Missed the first part of the stem. So I guess the prime part holds.
Current Student
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Has to (A)

Pick prime numbers and square them

KAPLAN STRATEGY = (Kan Always Pick Little Abstract Numbers)
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