Schindler's List, grocery lists, checklists, and even this list of lists: okay, you get it. There are many different types of lists. Are you ready for this? There are different types of math lists. These are called sequences. Stay with us, Shmoopers, and you'll not only know exactly what sequences are, but you will also be able to figure out exactly what numbers are allowed on each list, write out math-tastic rules describing these lists, and even know a couple of impressive terms used to categorize the lists. Once we're done there, we'll take the numbers in the lists and add 'em all up using this guy: ∑. He may look frightening, but he'll be cute and cuddly in no time. Trust us.