# Why does 0! = 1? (Index)

I’m using the Twelve Days of Christmas (and perhaps a few extra days besides) to do something that I should have done a long time ago: collect past series of posts into a single, easy-to-reference post. The following posts formed my series on how I explain to students that $0! = 1$.

Part 1: Multiplication and division.

Part 2: Combinatorics.