The effective range has been well discussed on the forums, and yes, the square root is all we need, plus 1 so the top value is in the range. It is not the half way point, though, but the crossover point if we take a list of factors and overlay it with a reverse of that list. Moot, though. Good that you picked up on this.
I agree that we should only iterate over odd numbers, and we can go down this rabbit hole to elliminate numbers divisible by 3, 5, 7, etc. Ultimately this will reduce to a range that includes only Prime numbers. We are a long way from working on that level of complexity. First we walk, then we run. Don’t let this distract you from the lesson plan, but add it to the back burner for extra study when you complete the track.