The Professor's Beloved Equation

is a novel by Yoko Ogawa set in modern-day Japan. It was published in August, 2003, by Shinchosha and was the first recipient of the Hon'ya Taisho award.

The story centers around a mathematician, "the professor," who suffered brain damage in a traffic accident in 1975 and since then can produce only 80 minutes' worth of memories, and his interactions with a housekeeper (the narrator) and her son "root" as the professor shares the beauty of equations with them.

The novel received the Hon'ya Taisho award, was adapted into a film version in January 2006, and after being published in paperback in December, 2005, sold one million copies in two months, faster than any other Shinchosha paperback.

The novel's bibliography lists the book "The Man Who Loved Only Numbers", a biography of the mathematician Paul Erdős. It has been said that Erdős was used as a model for the professor'.

Plot summary

The narrator’s housekeeping agency dispatches her to the house of the professor, a former mathematician who can remember new memories for only 80 minutes. She is more than a little frustrated to find that he loves only mathematics and shows no interest whatsoever in anything or anyone else. One day, upon learning that she has a 10-year-old son waiting home alone until late at night every day, the professor flies into a rage and tells the narrator to have her son come to his home directly from school from that day on. The next day, her son comes and the professor calls him by the name "root". From then on, their days begin to be filled with warmth.

Characters

;The professor:64 years old. A former university professor who specializes in number theory. He loves mathematics, children, and the Hanshin Tigers (especially Yutaka Enatsu, who was playing for the Tigers at the time of the professor’s accident and whose uniform number was 28, the second smallest perfect number). After being in an accident at the age of 47, he can retain new memories for only 80 minutes. He keeps important information on a memo paper which is attached all over his suits. He keeps baseball cards and memento photographs in a cookie tin. He has trouble interacting with other people and has a habit of talking about numbers when he does not know what else to say. He has a talent for reading things backwards and finding the first star in the sky.;The narrator:Housekeeper and single mother. Initially feels frustration at the professor, who shows interest only in mathematics, but through observing the professor's kindness and his passion for mathematics, comes to feel respect and affection for him. She first manages to connect with the professor when he discovers that her birthday is February 20 (220), which is an amicable number with the number 284, which is imprinted on the underside of his watch, which he received as the University President's Award for a thesis he wrote in university on transcendental number theory. Cannot pronounce the title of the "Journal of Mathematics" (to which the professor submits contest entries) very well, so she refers to it as "Jaanaru obu." Gives the professor a Yutaka Enatsu baseball card as a birthday present.;Root:Ten years old. Son of the narrator. The professor refers to him as "root" on account of the top of is head being flat like a √ symbol. Is a fan of the Hanshin Tigers, and gets the professor to repair his radio so that they can listen to baseball broadcasts together. Eventually becomes a junior high school mathematics teacher.;The Widow:Sister-in-law of the professor (wife of the professor's brother). Cannot walk well, as a result of a traffic accident.

Mathematics Terminology that occurs in Story

*root
*imaginary number
*factorial
*amicable number
*prime number
*twin prime
*perfect number
*abundant number
*deficient number
*triangular number
*Ruth-Aaron pair
*Mersenne prime
*Napier's constant
*Euler's formula
*Fermat's Last Theorem
*Artin's conjecture

Film

A fil of the novel was released January 21, 2006 that was directed by Takashi Koizumi.

In contrast to the original work, which is told from the perspective of the narrator, the film is shown from the perspective of the 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.