15 has more than exactly two factors (1, 3, 5, and 15), therefore it is composite.
17, 19, and 23 each have exactly 2 factors (1 and the number itself), so they are primes.
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15 is composite number 17, 19 and 23 are prime numbers.
15!
No
56 + 17 = 73 The only factors of 73 are 1 and itself. It is a prime number, not a composite number.
It is prime