why is 1 not considered a prime number?

I understand how you got the correct answer, but am confused as to why 1 was excluded.

@amusingminnow Great question! So, by definition, composite numbers are numbers that have more than \(2\) factors, and prime numbers are numbers that have exactly \(2\) factors: \(1\) and itself. The thing with \(1\) is that it only has one factor: \(1!\) so, it's neither prime nor composite.
\(1\) is just a unit, so it's called a unit sometimes.