Arima Yoriyuki

In this Japanese name, the family name is Arima.

Arima Yoriyuki (有馬 頼徸, December 31, 1714 – December 16, 1783) was a Japanese mathematician of the Edo period. He was the lord of Kurume Domain and approximated the value of $\pi$ and its square, $\pi^2$. In 1766, he found the following rational approximation of pi, correct to 29 digits:

$\pi\approx\frac{428224593349304}{136308121570117}=3.14159265358979323846264338327(569...)$