2
19 is prime.
None of them are prime numbers
21 is the product of two prime numbers, three and seven. A prime number is defined as a number divisible only by one or itself. So ... NO ... 21 is not a prime number.
23 is a prime number.
No 21 is not a prime number because it has more than two factors therefore it is a composite number
21 is not a prime number.
number 21 is prime
21 is a composite number, not a prime, having prime factors 3x7.
The number 3 is prime and has only one factor. 3 = 31 A better example of exponents in factoring would be a composite number such as 18: 18 = 2 x 3 x 3 18 = 21 x 32
Only 23 is a prime number.
19 and 23 are prime.
18 has prime factors 3 & 2 whereas 21 has prime factors 3 & 7.