  The inner two planets around the 55 Cancri were found to be trapped in the
3:1 mean motion resonance. In this paper, we study the dynamics of this
extra-solar planetary system. Our numerical investigation confirms the
existence of the 3:1 resonance and implies a complex orbital motion. Different
stable motion types, with and without the apsidal corotation, are found. Due to
the high eccentricities in this system, we apply a semi-analytical method based
on a new expansion of the Hamiltonian of the planar three-body problem in the
discussion. We analyse the occurrence of the apsidal corotation in this mean
motion resonance and its influence on the stability of the system.
