This program finds prime numbers manually

this program works by first asking for a positive integer say 16. then it creates an array ranging from 2 to 16. next all the numbers are divided by 2 and all that return back a integer are deleted from the array except for 2. example 4/2 =2, 4 will be deleted. after this, this same pattern continues with 3 and so on until the array is dived by ceil(sqrt(n)) so for the case of n=16, 2 and 3 can root out all of the non primes