An analytical exercise
  This is a translation into English from the original Latin of Leonhard Euler's Exercitatio analytica, Nova Acta Academiae Scientarum Imperialis Petropolitinae 8 (1794), 69-72; E664 in the Enestrom index. In it Euler uses the infinite product identity for sin to prove some properties of the series for the Riemann zeta function for even n. 
Leonhard Euler