Takebe Kenkō

Takebe Katahiro, also known as Takebe Kenkō, was a Japanese mathematician and cartographer of the Edo period, born in 1664 and dying on 24 August 1739. He was the favourite student of Seki Takakazu and is considered to have extended and disseminated Seki's work. In 1706 he was offered a position in the shogunate's department of ceremonies, and in 1719 he completed a new map of Japan that was highly valued for its quality and detail, which brought him rank and better positions under the shogun Yoshimune. He played a critical role in developing the enri or circle principle, a crude analogue of Western calculus, made charts of trigonometric functions, and in 1722 found the power series for the square of arcsine, fifteen years before Euler. He used Richardson extrapolation in 1695, two centuries before Richardson, and computed 41 digits of pi.