  We establish Manin's conjecture for a cubic surface split over Q and whose
singularity type is 2A_2+A_1. For this, we make use of a deep result about the
equidistribution of the values of a certain restricted divisor function in
three variables in arithmetic progressions. This result is due to Friedlander
and Iwaniec (and was later improved by Heath-Brown) and draws on the work of
Deligne.
