All prime numbers have only two factors.
That is 1 & the number itself.
Hence 1 is neither considered as a prime number nor a compound
Another fact on prime numbers are,
All prime numbers are odd numbers except 2.eg..11, 13, 17, 19, 23......
But all odd numbers are not prime numbers. Eg 9, 15, 21, 27, 33, 35 39 etc.