When a number is divisible by only one and itself, then it is a prime number. The prime numbers cannot be factorised as they are not divisible. The divisible numbers are called composite numbers. 1 is neither prime nor composite.
How do we get to know if a number is prime or not?
To calculate we need to find the factors of the number. Take for example 11, 11 is divisible only by 1 and itself. Since it has only two factors, it is a prime number.
Question 1: Find if 53 is a prime number or not ?
The factors of 53 are 1 and 53.
So 53 is only divisible by 1 and 53.
So, 53 is a prime number.
Question 2: Check if 64 is a prime number or not?
Solution. The factors of 1, 2, 4, 16, 8.
Hence it is a composite number and not a prime number.