I have the following problem: What is the sum of the first 40 positive odd integers? I look at the solution, and it says that "The sum of the first 40 positive odd integers is ##1 + 3 + 5 + \dotsm + 77 + 79##. And then it goes on with the solution. My question is, how do I find that 79 is the 40th positive odd integer? Do I have to just write them all down until I get to the 40th one?