  We report results of collisional N-body simulations aimed to study the
N-dependance of the dynamical evolution of star clusters. Our clusters consist
of equal-mass stars and are in virial equilibrium. Clusters moving in external
tidal fields and clusters limited by a cut-off radius are simulated. Our main
focus is to study the dependence of the lifetimes of the clusters on the number
of cluster stars and the chosen escape condition.
  We find that star clusters in external tidal fields exhibit a scaling problem
in the sense that their lifetimes do not scale with the relaxation time.
Isolated clusters show a similar problem if stars are removed only after their
distance to the cluster centre exceeds a certain cut-off radius. If stars are
removed immediately after their energy exceeds the energy necessary for escape,
the scaling problem disappears.
  We show that some stars which gain the energy necessary for escape are
scattered to lower energies before they can leave the cluster. Since the
efficiency of this process decreases with increasing particle number, it causes
the lifetimes not to scale with the relaxation time. Analytic formulae are
derived for the scaling of the lifetimes in the different cases.
