You have an unlimited supply of red, blue, and green plates in your kitchen, and are going to create a stack of exactly n of these plates. However, your roommate has a rule that any blue plate in a stack must have a green plate directly on top of it in the stack.

Write a recurrence counting the number of different possible color orderings for the stack of n plates which are allowed by your roommate. Dont forget to state the base case(s). You do not need to solve your recurrence.