It's been a while since I last wrote up a specific lesson idea so when my friend Garth asked about recursion ideas I thought I'd write this one up. This is a unit I used to teach in my intro class at Stuy using Racket (nee Scheme) but I coded up a quick and dirty Python version. Recursion is a polarizing topic. Some people love it, others hate it. I'm sure the usual suspects of intro recursion problems doesn't help.