Prime Number Finder using C++

The isPrimeNumber() function determines if a number is prime by following an efficient approach. 

First, it checks if the number is less than or equal to 1, returning false since numbers less than or equal to 1 are not prime. If the number is 2 or 3, it returns true because both are prime numbers. 

Next, the function checks if the number is divisible by 2 or 3—if so, it returns false, as any number divisible by these is not prime (except 2 and 3 themselves). 

For larger numbers, the function uses a loop starting from 5 and increments by 6. This optimization checks divisibility only by numbers of the form 6k ± 1 skipping multiples of 2 and 3 to reduce unnecessary checks. If the number is divisible by any of these, the function returns false; otherwise, it returns true, indicating the number is prime. 

The loop runs up to the square root of the number to further optimize performance.