Fermat's and Euler's Theorems

Pierre de Fermat (1601–1665) was a public official in the French city of Toulouse, and in his spare time was one of the greatest mathematicians of the seventeenth century. Fermat's “little theorem”, as generalized by Euler a century later, is perhaps the first theorem in what is now known as group theory. It also has some remarkably interesting applications. We present Fermat's theorem and related theory in this chapter and some applications in the next.