  A centrally essential ring is a ring which is an essential extension of its
center (we consider the ring as a module over its center). We give several
examples of noncommutative centrally essential rings and describe some
properties of centrally essential rings. V.T.Markov is supported by the Russian
Foundation for Basic Research, project 17-01-00895-A. A.A.Tuganbaev is
supported by Russian Scientific Foundation, project 16-11-10013.
