Another question I thought of was, "What is the history of prime numbers; where did they come from?" This is another topic that would be great to share with my own high school math class someday. Once again, Wikipedia gave me some answers:

"There are hints in the surviving records of the ancient Egyptians that they had some knowledge of prime numbers: the Egyptian fraction expansions in the Rhind papyrus, for instance, have quite different forms for primes and for composites. However, the earliest surviving records of the explicit study of prime numbers come from the Ancient Greeks." (Wikipedia)

Does anyone else have any other interesting facts about the history of prime numbers to add to this? Thanks!