So like always, pause the video and see if you can work through this on your own. So when you look at the sum, it's clear you're starting at two, you're adding three each time, and we also are dealing with you have four total terms. Now we could try to construct an equation here or an expression using sigma notation, but instead what I like to do is look at our options. We really only have to look at these two options here and expand them out. What sum would each of these be? Well this is going to be the same thing as. We're starting at n equals one.