How many numbers ≤ 500 have exactly 3 factors?

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• A 7
• B 8
• C 9
• D 10

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Answer: B. 8

p^2 <= 500 => p <= sqrt(500) ≈ 22

Prime numbers <= 22:
2, 3, 5, 7, 11, 13, 17, 19

Total = 8

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