  The mass-imbalanced fermionic mixture is studied, where $N\le5$ identical
fermions interact resonantly with an impurity, a distinguishable atom. The
shell structure is explored, and the physics of a dynamic light-impurity is
shown to be different from that of the static heavy-impurity case. The energies
in a harmonic trap at unitarity are calculated and extrapolated to the
zero-range limit. In doing so, the scaling factor of the ground state, as well
as of a few excited states, is calculated. In the $2 \le N \le 4$ systems, pure
$(N+1)$ Efimov states exist for large enough mass ratio. However, no sign for a
six-body Efimov state in the $(5+1)$ system is found in the mass ratio
explored, $M/m \le 12$.
