The first ten prime numbers are:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29
The list of prime numbers is something to memorize or have on a reference sheet. A prime number has factors of 1 and itself only.
For instance, 17 is prime because the only factors are 1 and 17.
In contrast, 18 is not prime (aka composite) because it has factors 1, 2, 3, 6, 9, and 18.
The value 1 is not prime because it needs exactly 2 factors of 1 and itself. The "itself" value has to be different from 1, as shown in the example talking about the prime 17.
The value 1 is also not considered prime because it would break the fundamental theorem of arithmetic. This theorem says that any positive integer can be factored uniquely into primes (where we ignore the order). The key word "uniquely" would not be the case if we allowed 1's into the mix. For example, the factorization 12 = 2*2*3 would clash against 12 = 1*2*2*3 and also 12 = 1*1*2*2*3 and so on.