Memento
The Housekeeper and the Professor, Yoko Ogawa, 2009
A charming little novel from Japan. A single mom raising a 10 year old boy works as a housekeeper at an agency. Her new assignment is with a mathematics professor who has already gone through eight previous housekeepers at the agency. She discovers the professor suffered brain damage from an auto accident many years ago and has a memory that lasts exactly 80 minutes. To remind himself of important things, the professor pins little notes to his suit.
Pierre de Fermat Stamp 
For the new housekeeper, he draws a rough sketch and pins it along all the other notes. She remains nameless in the story. The professor’s mathematical skills remain undiminished, and though he can no longer teach, he spends his time solving mathematical puzzles published in the journals. He earns prizes and awards with his solutions. When the professor learns the housekeeper has a son who is left home alone after school, he insists she bring him to the professor’s house. The boy has a flat head, reminding the professor of the square root sign and he calls the boy “root” the only name ever used in the novel. The boy and professor share an interest in Japanese professional baseball, albiet the professor’s interest is purely for the statistics of the game. The professor’s knowledge of baseball is frozen in 1975, the time of his accident. Both housekeeper and son become interested in mathematics to the point that the housekeeper, who never finished high school, starts going to the library to find formulas she has seen the professor write and learn about great unsolved problems. Ogawa carefully researched her mathematics subject including many of the mysterious and magical aspects such as prime numbers and Fermat’s last Theorem (solved only recently).
Sir Andrew John Wiles Proved Fermat’s Theorem 