Factorial Factory
BOOSH
As some of the comments say, a number of these could be really useful in understanding/expressing series. Unfortunately, I’ve never heard of any of these being explicitly taught.
Yo Dawg, I Herd U Like Factorials
Have you ever wondered why zero factorial (0!) equals 1? One of my students sent me a link to this explanation. It’s pretty intuitive when explained this way.
Eigenblogger 