To determine if 399 is a prime number or a composite number, we simply look at the factors for 399.
If the factors of 399 are only 399 and 1, then we know that 399 is a prime number. Otherwise, 399 is a composite number.
To explain better, if 399 is only divisible by 1 and 399, then it is a prime number, and if 399 is divisible by more than 399 and 1, then it is a composite number.
The factors of 399 are as follows:
1, 3, 7, 19, 21, 57, 133, 399
Therefore, since 399 is divisible by more than one and itself, the answer to the
question "Is 399 prime or composite?" is highlighted in blue below.
composite
Is 400 prime or composite?
OK. Now you know that 399 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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