21: Permutations Last updated Save as PDF Page ID 83510 Jeremy Sylvestre University of Alberta Augustana 21.1: Factorials In counting, factorials come up a lot. 21.2: Definition We often want to count how many ways we can “mix up” the objects in a collection. 21.3: Counting Permutations For |A|=n, there are n! permutations on A. 21.4: Permutations of Subsets Sometimes we want to create an ordered list of a certain length from a larger pool of candidates. 21.5: Activities