Teacher and Traveler Sakuma Yōken: Fukushima’s Nineteenth-Century “Wasan” Math Master

A signpost shows the way to Sakuma Yōken’s former study, with rice paddies as far as the eye can see. (© Abe Haruki)

Sakuma Motomu displays photographs of his great-grandfather Sakuma Yōken. The photograph on the right shows Yōken as a young man, and the other shows Yōken in his final years. (© Abe Haruki)

The student registers preserved by the Sakuma family. At far right is the female name Toku. (© Abe Haruki)

Nakazawa Ichio of the Funehiki Sakuma Yōken Wasan Preservation Society (left) sits outside Yōken’s study with the mathematician’s great-grandson Motomu. In former decades the building had an attached dormitory. (© Abe Haruki)

Diagram and solution for the problem on Yōken’s sangaku. (Courtesy Nakazawa Ichio)

Top: Sangaku at Akitasan Ryūon’in temple (posted 1893). Bottom: Sangaku at Kobiragata Tenmangū temple (posted 1885). (© Abe Haruki)

Ganna Mamonova in Kyiv during an online interview. (Courtesy Abe Haruki)

A panel from Mamonova’s comic book Fun with Combinatorics, with art by Tatiana Denisenko. (Courtesy of Ganna Mamonova)

Ōsu Kannon. (© Pixta)