C problem

Question

I found this methode to check wether a number is prime ir not but i didn't get the meaning of that i*i ..?
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int isPrime(int n) {
for (int i = 2; i * i <= n; i++)
if (n % i == 0)
return 0;
return 1;
}
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Answer 1

It's just to make the function shorter, because if there is a number bigger than the square root of the number that is divisible by it, then there must be a number smaller than the square root.

It would perfectly work like this:
for (int i = 2; i < n; i++)...

(although this isn't perfect, because it will register 1 as a prime number too)