Fermat posed the problem of solving x 2 − N y 2 = 1 {\displaystyle x^{2}-Ny^{2}=1} as a challenge to English mathematicians (1657).
Fermat formulou o problema de resolver x 2 − N y 2 = 1 {\displaystyle \scriptstyle x^{2}-Ny^{2}=1} como un reto aos matemáticos ingleses (1657).