Euler and Number Theory

We give an account of the most important results obtained by Euler in number theory, including the main contribution of Euler, application of analysis to problems of number theory. We note an important role played in modern number theory by the function that was introduced by Euler and is called the Riemann zeta function. We also discuss Euler's works in other fields of science such as function theory and theory of music, as well as the relationship between music and mathematics.