  We study the evolution of the mass function in young and dense star clusters
by means of direct N-body simulations. Our main aim is to explain the recent
observations of the relatively flat mass function observed near the centre of
the Arches star cluster. In this region, the power law index of the mass
function for stars more massive than about 5-6 solar mass, is larger than the
Salpeter value by about unity; whereas further out, and for the lower mass
stars, the mass function resembles the Salpeter distribution. We show that the
peculiarities in the Arches mass function can be explained satisfactorily
without primordial mass segregation. We draw two conclusions from our
simulations: 1) The Arches initial mass function is consistent with a Salpeter
slope down to ~1 solar mass, 2) The cluster is about half way towards core
collapse. The cores of other star clusters with characteristics similar to
those of the Arches are expected to show similar flattening in the mass
functions for the high mass (>5 solar mass) stars.
