There are 6 letters in the word "autumn" so 6! = 6*5*4*3*2*1 = 720 represents the number of ways to arrange the letters (order matters)
Note how there are two letter "u"s here which can't be told apart. If we could tell them apart, then the answer would be 720. However, we can't tell them apart. So we're doubly counting things. To undo this, we divide by 2
