To determine if 645 is a prime number or a composite number, we simply look at the factors for 645.
If the factors of 645 are only 645 and 1, then we know that 645 is a prime number. Otherwise, 645 is a composite number.
To explain better, if 645 is only divisible by 1 and 645, then it is a prime number, and if 645 is divisible by more than 645 and 1, then it is a composite number.
The factors of 645 are as follows:
1, 3, 5, 15, 43, 129, 215, 645
Therefore, since 645 is divisible by more than one and itself, the answer to the
question "Is 645 prime or composite?" is highlighted in blue below.
composite
Is 646 prime or composite?
OK. Now you know that 645 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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