Q: Is 399 a Prime Number?
A: No, 399 is not a prime number.
A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 399 can be evenly divided by 1 3 7 19 21 57 133 and 399, with no remainder.
Since 399 cannot be divided by just 1 and 399, it is not a prime number.