To determine if 405 is a prime number or a composite number, we simply look at the factors for 405.
If the factors of 405 are only 405 and 1, then we know that 405 is a prime number. Otherwise, 405 is a composite number.
To explain better, if 405 is only divisible by 1 and 405, then it is a prime number, and if 405 is divisible by more than 405 and 1, then it is a composite number.
The factors of 405 are as follows:
1, 3, 5, 9, 15, 27, 45, 81, 135, 405
Therefore, since 405 is divisible by more than one and itself, the answer to the
question "Is 405 prime or composite?" is highlighted in blue below.
composite
Is 406 prime or composite?
OK. Now you know that 405 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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