Which ONE of the following describes a prime number?
A number greater than $1$1 that has more than two factors.
A number that has a factor of $1$1.
A number that has at most two factors: itself and $1$1.
A number greater than $1$1 that has exactly two factors: itself and $1$1.
Which ONE of the following describes a composite number?
Is $5$5 prime or composite?
Is $21$21 prime or composite?