First of all u need to knw what is prime no a no which is either divisible by 1 or itself is known as prime no. for eg- 1,2,3,5,7,9,11,13,17,19 and so on which have only two factors 1 and they itself. hope u got it!!!!!
1 1 1
The no which is divided by itself and 1 is known as prime no.
1 5 1