Ludolph van Ceulen was 56 when he published 20 digits of $\pi$, and he later expanded this to 35 digits. He was appointed as a professor when he was 60. Computing 35 digits of $\pi$ may seem easy now, but he did it before calculus. In some German universities $\pi$ was called "Ludolph's number" even into the 20th century.
Michael Renardy
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