1 + 2 + 3 + 4 + · · ·

Okay kiddo, so let's start with the symbol '+' which means we're adding things together. Now, if we start with the number 1 and add 2 to it, we get 3. Then, if we add 3 to 3, we get 6. We can keep doing this over and over again by adding each consecutive number to the sum we've already calculated, like this: 1+2=3, 3+3=6, 6+4=10, and so on. This pattern keeps going forever and ever, we just keep adding one more number every time. And that's what we call "an infinite sum." This particular infinite sum, "1+2+3+4+...", starts with 1 and adds all the natural numbers (the numbers that come next, like 2, 3, 4, and so on) forever and ever. It's a little bit like counting in a never-ending way!