  Let $p$ be a prime. We discuss $p$-adic properties of various arithmetical
functions related to the coefficients of modular form and generating functions.
Modular forms are considered as a tool of solving arithmetical problems.
Examples of congruences between modular forms modulo $p$ and modulo $p^n$ are
given, and the use of a computer for the study of modular forms is illistrated.
