You don’t have to be a genius or complete any assignments. All of these books are fairly accessible to the average reader.
I read the majority of them in high school, and they set me (a dyslexic student with undiagnosed adhd) up for a lifetime love of mathematics.
Many of these books could also be categorized as popular science or history books. A couple of them, such as Surreal Numbers and Flatland, are actually fiction!