  Exact analytical expressions in terms of generalized confluent hypergeometric
functions for the transition amplitudes of neutrino oscillations in presence of
matter are computed for an arbitrary number of species. The density of matter
is assumed to be exponentially decaying. The results can be used for the
description of matter-induced neutrino oscillations in the Sun which can take
place when the solar neutrinos propagate radially from the interior to the
surface. Expressions are particularly simple in the limit of infinite
propagation time as is suitable for the case of detection at Earth. PACS:
14.60.Pq, 02.30.Gp, 02.30.Hq
