Thomas Fantet de Lagny

Thomas Fantet de Lagny (1660 to 1734) was a French mathematician well known for his contributions to computational mathematics and for calculating pi to 112 correct decimal places. The son of a royal official in Grenoble, he became passionate about mathematics at a Jesuit college in Lyon, studied law for three years at Toulouse and in 1686 went to Paris as a mathematics tutor to the Noailles family, where he collaborated with de l'Hospital and published his first papers. On 11 December 1695 he was named an associate of the Académie Royale des Sciences, and in 1697 he became professor of hydrography at Rochefort for sixteen years. Returning to Paris in 1714, he became a librarian at the Bibliothèque du roi and was deputy director of the Banque Générale from 1716 to 1718. He received a pension from the academy in 1719, became a pensionnaire in 1723 in place of Pierre Varignon and had to retire in 1733. In 1719 he calculated pi to 127 decimal places with Gregory's arctangent series, of which 112 were correct, a record that stood until Jurij Vega found 126 correct digits in 1789.