Question

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How many numbers less than 30 have an odd number of factors?

Answer 1

• 5 numbers

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Only the perfect squares have odd number of factors.

Example

• 1 ⇒ 1 One factor
• 4 ⇒ 1, 2, 4 Three factors
• 16 ⇒ 1, 2, 4, 8, 16 Five factors

Perfect squares less than 30 are

• 1, 4, 9, 16, 25 - total 5 numbers