Prime number is a positive natural number that has only two positive natural number divisors - one and the number itself.
Prime numbers are subset of natural numbers. A natural number is a positive natural number that has at least one positive divisor other than one or itself.
The number 1 is not a prime number by definition - it has only one divisor.
The number 0 is not a prime number - it is not a positive number and has infinite number of divisors.
The number 15 has divisors of 1,3,5,15 because:
15/1=15
15/3=5
15/5=3
15/15=1
So 15 is not a prime number.
The number 13 has only two divisors of 1,13.
13/1=13
13/13=1
So 13 is a prime number.
List of prime numbers up to 100:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, ...
The number 0 is not a prime number.
Zero is not a positive number and has infinite number of divisors.
The number 1 is not a prime number by definition.
One is has one divisor - itself.
The number 2 is a prime number.
Two has 2 natural number divisors - 1 and 2:
2 / 1 = 2
2 / 2 = 1