To determine if 639 is a prime number or a composite number, we simply look at the factors for 639.
If the factors of 639 are only 639 and 1, then we know that 639 is a prime number. Otherwise, 639 is a composite number.
To explain better, if 639 is only divisible by 1 and 639, then it is a prime number, and if 639 is divisible by more than 639 and 1, then it is a composite number.
The factors of 639 are as follows:
1, 3, 9, 71, 213, 639
Therefore, since 639 is divisible by more than one and itself, the answer to the
question "Is 639 prime or composite?" is highlighted in blue below.
composite
Is 640 prime or composite?
OK. Now you know that 639 is a composite number. Use our logic above and see if
you can figure out if the next number on our list is prime or composite before you check your answer.
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