The Housekeeper and the Professor by Yoko Ogawa

The Housekeeper and the Professor

This story takes place in Japan and is told from the viewpoint of a woman who is a young single mother who works as a housekeeper. She is assigned to work in the little two room cottage inhabited by a math professor who had been in a car accident. He was only able to remember events that occurred before the accident and the previous 80 minutes. Every day she had to introduce herself to him because he did not know he had already met her. He kept notes to himself pinned to his jacket including one to remind himself he could only remember the last 80 minutes. 

Eventually she brought her 10-year old son to the professor's house after school and the professor called him Root because the flat top of his head reminded him of the square root sign. Root and the professor found they both loved the same baseball team even though the professor only remembered the players from before the accident.

What was fun was how the professor shared his love of mathematics with the housekeeper and her son. He taught them about prime numbers and i, the square root of -1. This story was enjoyable for the shared joy of math as well as the challenge of working with a person who has had a brain injury.