Claude Gaspar Bachet Sieur de Méziriac[1] (9 October 1581 – 26 February 1638) was a French mathematician and poet born in Bourg-en-Bresse, at that time belonging to Duchy of Savoy.

He also discovered means of solving indeterminate equations using continued fractions, a method of constructing magic squares, and a proof of Bézout's identity.

[3] Bachet wrote the Problèmes plaisans et délectables qui se font par les nombres[note 1] of which the first edition was issued in 1612, a second and enlarged edition was brought out in 1624; this contains an interesting collection of arithmetical tricks and questions, many of which are quoted in W. W. Rouse Ball's Mathematical Recreations and Essays.

[2][4] He also wrote Les éléments arithmétiques,[note 2] which exists in manuscript; and a translation, from Greek to Latin, of the Arithmetica of Diophantus (1621).

The same text renders Diophantus' term παρισὀτης as adaequalitat, which became Fermat's technique of adequality, a pioneering method of infinitesimal calculus.