They don't.
21 has two prime factors.
42 has three prime factors.
Usually, but not necessarily and not if they're prime. All prime numbers have the same number of factors.
All prime numbers have only two factors whereas all composite numbers have more than two factors.
All numbers have factors. Some factors are prime numbers. A prime factor is a factor that is a prime number. A common prime factor is a prime factor that appears on the list of factors of two or more given numbers.
All composite numbers are not prime numbers because they have more than two factors
All numbers have factors. Some factors are prime numbers. These are known as prime factors.
All numbers that only have one and itself as factors are prime. Therefore, to tell if a number is prime simply find it's factors. If it has more than two factors than it is not a prime number.
Prime numbers have only two factors whereas composite numbers have more than two factors and that 1 is not considered to be a prime or composite number but it is a factor of all other numbers.
Usually, but not necessarily and not if they're prime. All prime numbers have the same number of factors.
Yes, all prime numbers have only two factors
All numbers that only have one and itself as factors are prime. Therefore, to tell if a number is prime simply find it's factors. If it has more than two factors than it is not a prime number.
All prime numbers have two factors.
All numbers that only have one and itself as factors are prime. Therefore, to tell if a certain number is prime simply find it's factors. If it has more than two factors than it is not a prime number.