factors of 21: 3, 7
prime factors of 21: 3, 7
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21 has two prime factors.
No, 21 and 23 are not twin prime numbers. Twin primes are pairs of prime numbers that differ by 2, such as 3 and 5, or 11 and 13.
The prime numbers between 10 and 21 are 11, 13, 17, and 19.
There are 21 two-digit prime numbers.
None of them is a prime number.