The story is about an old professor and a special bond that develops between the professor and his housekeeper. The professor has a peculiar problem that he cannot remember anything beyond 80 minutes. His memory loss caused by a certain accident in his middle age leads to a strange life that he leads. Since he cannot remember anything beyond 80 minutes, he is forced to write short notes and pin it up on his suit so that he can glance at them everyday and remember stuff. His sister-in-law generously takes care of him and provides him with basic amenities like food , shelter and a study room. The professor despite his old age continues doing math. To take care of the cooking,cleaning and other household activities, his sister-in-law appoints a housekeeper.

Since the professor has no memory beyond the last 80 minutes, the housekeeper has to introduce herself everyday to the professor to gain entry in to the house. The professor has a peculiar way of letting her in to the house. He would ask a few questions whose answers are numbers like her shoe-size, her date of birth and allows her to enter the house. The housekeeper brings along her son to the work, at Professor’s request . The Professor soon develops a liking toward the kid and slowly starts taking time to teach him some basic math. He fondly calls him “root” , because of his rather flat head that resembles a square root sign.

Math becomes the focus of most of the conversations in the house. The housekeeper is sucked in to the infectious enthusiasm that the professor displays. Even though she is supposed to merely take care of household chores, she tries to strike conversation with the professor whenever possible and in the process learns about a whole lot of math stuff like perfect numbers, amicable numbers, prime numbers, fascinating square root sign, 0 (queen of numbers), triangular numbers, Euler’s equation, the way all the primes can be divided exactly in to two categories etc. Professor’s liking towards the kid makes him spend more time with him teaching math in such a way that it brings an element of delight and surprise even in some mundane math concepts.

The book ends with Professor’s death and the Housekeeper’s son becoming a math faculty at a local college. Well, as the story has a bit of melodrama in it, it is no wonder that this book was made in to Japanese film titled “The Professor and His Beloved Equation”.

Via Wikipedia :

The Professor’s Beloved Equation is a Japanese film released January 21, 2006 and directed by Takashi Koizumi. It is based on the novel The Housekeeper and the Professor.

In contrast to the original work, which is told from the perspective of the narrator, the film is shown from the perspective of a 29 year old root as he recounts his memories of the professor to a group of new pupils. Though there are a few differences between the film and the original work (for example, the movie touches on the relationship between the professor and the widow while the book does not give much detail), the film is generally faithful to the original.