Why is $1$ not a prime number? Why is $1$ not considered a prime number?

Or, why is the definition of prime numbers given for integers greater than $1$?
One of the whole "points" of defining primes is to be able to uniquely and finitely prime factorize every natural number.

If 1 was prime, then this would be more or less impossible.
The Question should be _&quot;Why is the word $prime$ used only for a positive non-invertible indecomposable integer?&quot;_The Answer is that Positive-NonInvertible-Indecomposable-Integer is too long, except in German. If you need a name for numbers that are either prime or $1$, you may invent one!