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The current implementation starts the loop from i = 3, iterating up to the square root of _num. It checks whether _num is divisible by i for each value of i in the loop. If _num is divisible by any number in this range, _notAPrime is set to true, indicating that _num is not a prime number.

It is not necessary to start the loop from i = 2 because the code is skipping even numbers by incrementing _num by 2 (_num += 2) at the end of the method. If _num starts from an odd number (which is the case here), there is no need to check divisibility by even numbers in the loop because if a number is divisible by an even number other than 2, it won't be a prime number. Starting the loop from i = 3 and incrementing by 2 (i += 2) is enough for checking the primality of _num.

Since even numbers other than 2 cannot be prime, you could further optimize the loop by starting from i = 3 and incrementing by 2, skipping even numbers altogether.

So, if we start the loop from 2, then that would still work correctly, and starting from 3 and incrementing by 2 is more efficient when dealing with odd numbers as it skips unnecessary even numbers.

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