Please answer the question

Let any positive number n is written as bmultiplication of two factors:

n= ab

Note that is both a and b are exactly equal to n^1/2 , then they multiply to give n.

But if any of them is less than n^1/2 , other has to be greater than n^1/2  to compensate.

So if the number p is a prime, then checking that it cannot be divided by any prime less than or equal to n^1/2  is a sufficient condition for primality testing.