YES
They are all prime numbers except for 15 21 25 and 27 which are composite numbers
hcf(10, 21) = 1 ⇒ 10 & 21 relatively prime hcf(12, 54) = 6 ⇒ 12 & 54 not relatively prime hcf(15, 27) = 3 ⇒ 15 & 27 not relatively prime hcf(21, 38) = 1 ⇒ 21 & 38 relatively prime
NO. Not all odd numbers are prime like 9, 15, 21, 27,... because they have other factors aside from 1 and itself.
No, neither of them are.
No.
9, 15, 21, 25 and 27 aren't .. because they have more than two divisors.
It is 23
A prime number has exactly two factors, 1 and the number itself. The factors of 21 are 1, 3, 7, and 21, and the factors of 27 are 1, 3, 9, and 27. Since 21 and 27 have more than 2 factors, they are composite numbers.
13,19.
They are 13 and 19 which are prime numbers
It is 31 because it has only two factors which are itself and one
No, there are many odd numbers that are not prime: 9, 15, 21, 25, 27, etc. However, 2 is the only even number that is prime, since all other even numbers are divisible by 2.