Three nines. You find them at the end of things: on the final line of the list you just closed, on the count that rounds itself off, on the chapter where the book reaches its end. The triple carries a sense of completion the eye registers before the mind arrives at the word for it.
Nine is the last digit; after it the count starts over. So the triple reads as an ending already in progress, not one being announced. There is nothing dramatic in it. Endings of this kind are mostly administrative: the thing stopped mattering a while back and the paperwork is catching up.