To determine if 999 is a prime number or a composite number, we simply look at the factors for 999.
If the factors of 999 are only 999 and 1, then we know that 999 is a prime number. Otherwise, 999 is a composite number.
To explain better, if 999 is only divisible by 1 and 999, then it is a prime number, and if 999 is divisible by more than 999 and 1, then it is a composite number.
The factors of 999 are as follows:
1, 3, 9, 27, 37, 111, 333, 999
Therefore, since 999 is divisible by more than one and itself, the answer to the
question "Is 999 prime or composite?" is highlighted in blue below.
composite
Is 1000 prime or composite?
OK. Now you know that 999 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.

