4.1 Extras!
Instructions
Watching the following video is optional, but you may find them interesting.
- What is \(0!\)? (Numberphile)
Length: 7m 53s
![](https://i3.ytimg.com/vi/Mfk_L4Nx2ZI/maxresdefault.jpg)
![](/images/Icons/YouTubeOverlay.png)
Watching the following video is optional, but you may find them interesting.