Wasan—meaning Japanese mathematics—is a unique form of mathematics that was developed in the Edo (1603 -1867) period while Japan was isolated from the rest of the world. During this time, mathematics underwent an extraordinary evolution in parallel to, and in many ways, beyond that of the Western world. Everyone, from the nobility to children in farming villages, grew to enjoy mathematics as if it were a game or sport and competed to solve complex mathematical puzzles.

Led by Seki Tkakazu (1642 -1708) and Takebe Katahiro (1664 -1739), many world-class mathematicians contributed to the amazing world of wasan. Jinkōki (1643), a wasan textbook written by Yoshida Mitsuyoshi in 1627, became a bestseller and was said to have been found in “every household.” It contained very difficult problems, known as idai, that were presented as challenges, and attempting to solve these complex problems became a popular pastime. With independent discoveries of π and other famous mathematical formulae devised during this time, we have come to realize that many of these problems were on a world-class level.

This eye-opening book introduces many of the key figures found in the world of Edo-period mathematics along with each of their contributions to the field of mathematics. With evocative descriptions of contemporary Japanese society, the puzzles and challenges come alive and illustrate how mathematics was a form of entertainment rather than a chore forced upon students in order to pass examinations. Placing the reader into this mindset, the author presents his own idai as a challenge for the reader to discover a way in which wasan can contribute to the future of mathematics.