  Incompressible (magic) states of vertically coupled quantum dots submitted to
strong magnetic fields such that only the lowest Landau level is relevant are
studied within an exact diagonalization calculation for N=3, 5 and 6,
electrons. We find that the sequences of total angular momentum M for which
incompressible states exists depend on the interplay between the inter-dot
hopping parameter \Delta_t and the inter-dot distance d. For d of the order of
the magnetic length and for all values of \Delta_t, we conclude that, in
contrast to previous claims, the incompressible states appear at magic values
of M which do not differ from those obtained for a single dot, namely
M=N(N-1)/2+jN where j is a positive integer number. For large inter-dot
distance and simultaneously small inter-dot hopping parameter, new sequences of
magic values of $M$ are observed. These new sequences can be easily understood
in terms of a transition regime towards a system of two decoupled single dots.
However, important differences in the nature of the incompressible ground
states are found with respect to those of a single dot.
