We had fun with this on Twitter a while ago. I’m just posting on the blog for the more permanent record.
If I end a sentence with a factorial, do I need a period?
That is, which of the following should it be?
(1) The number of ways to arrange 4 cats in a parade is 4!.
(2) The number of ways to arrange 4 cats in a parade is 4!
UPDATE: After being taken to task for a missing question mark by one Chris Lusto, I have corrected the error. I regret the oversight in a post about punctuation!