Index N represents "skip N elements". That gives you very easy additive/subtractive behaviour, unlike "how many numbers are there from 7 to 17?" scenarios. Sur

Index N represents "skip N elements". That gives you very easy additive/subtractive behaviour, unlike "how many numbers are there from 7 to 17?" scenarios. Sure, 17-7 gives you 10, but that's not the final answer, you have to add 1 to get the right answer, 11. Sorry, no, you actually subtract 1 and the right answer is 9. Wait, no: 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, okay, 11 in total, so you have to add 1, got it right the first time.