I am working on the Programming Exercises of Chapter 2 on the Starter Kit, and I am struggling with #3: Write a program that computes the sum of the first N positive integers, for a user-supplied value of N.

I got the part of inputting for N down, but I have no idea how to make the Summation function work in the program. I can do it on the homescreen, but it doesn't appear in code the same way. I have a TI-84+CE, and the Summation function is found after you push MATH, the character with jagged lines. I can't find anything on this site about the function.