I think I picked up this book solely because it has Euler's equation on the cover, but Yoko Ogawa has written one of the loveliest stories about strangers becoming friends I've ever read. This is a short little book, but it's got a lot of heart. It's about a single mother who's hired to work as a housekeeper for a brilliant former math professor who only has a working memory span of 80 minutes due to a brain injury that happened decades before the book begins. Things are awkward at first. He's gone through several housekeepers already that didn't work out because of all the difficulties he has as a result of his amnesia, and he's understandably frustrated by having to rely on clipping notes to his clothing about all the things he constantly has to remind himself of. But the friendship that develops between the professor and the housekeeper as he uses math and numbers as a bridge to span the divide between himself and people he's never sure if he's met before is truly special, as is the heartwarming bond that develops between him and the housekeeper's ten-year-old son. I really enjoyed this story, although it left me with a lingering feeling that it lacked resolution.