My war on Logic

I am not sure why this popped in my head the other day but I knew about sequels(which i found out is called a duology) or a trilogy. I just never thought about what 4 or more works or art, movies, or books are called. Gabe responded to my gmail status message with the correct answer of Tetralogy. I had never heard that word before. A few people post Quadlogy though from research that was made up by 20th century fox to start marketing box sets of DVD's. I found this link below which I found interesting. They have links for sets of 2, 3, 4,5 and 7 works. I guess people don't ever do things as a series of 6 that they needed to make a word about it. I just found that kind of interesting.

http://www.answers.com/topic/heptalogy