The average order of a class of arithmetic functions over arithmetic progressions with applications to quadratic forms.
Let be the Riemann zeta-function. If and , then it is known that the inequality is valid except at the zeros of . Here we investigate the Lerch zeta-function which usually has many zeros off the critical line and it is expected that these zeros are asymmetrically distributed with respect to the critical line. However, for equal parameters it is still possible to obtain a certain version of the inequality .
In the paper, we give a survey of the results on the approximation of analytic functions by shifts of Hurwitz zeta-functions. Theorems of such a kind are called universality theorems. Continuous, discrete and joint universality theorems of Hurwitz zeta-functions are discussed.