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theres only one even Prime number, thats 2

prime numbers can only be divided by themselves, and 1

21, divisible by 3 or 7, so no

28 even number other than 2, so no

15, divisible by 3 or 5, so no

17 divisible only by itself and 1, so yes

28, even number, other than 2, so no

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Q: Are 21 28 15 17 and 28 prime numbers?
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