A prime number is a number that only has one factor; one and itself. It is a list of odd numbers with the exception of two. Sure! Most students wonder why two is a prime number. Well, two contains only two factors, one and itself. Composite numbers on the other hand have more than one factor. And they also include a set of odd numbers and even numbers. The main rule is that they have more than one factor. For this exercise, students get to play the zombie math board game. For second grade, third grade, fourth grade, fifth grade, sixth grade and seventh grade students.