  Evolution of the reduced density matrix for a subsystem is studied to
determine deviations from its Markov character for a system consisting of a
closed chain of $N$ oscillators with one of them serving as a subsystem. The
dependence on $N$ and on the coupling of the two subsystems is investigated
numerically. The found deviations strongly depend on $N$ and the coupling. In
the most beneficial case with $N-1=100$ and the coupling randomized in its
structure the deviations fall with the evolution time up 3\%. In other cases
they remain to be of the order 30\% or even more.
