Fermion parity of phases supporting multiple Majorana modes in a superconducting nanowire

The fermion parity of the ground state is determined in various topological phases of the semiconducting nanowire under external magnetic field with proximity-induced superconductivity and strong spin-orbit interaction. Electron hopping as well as spin-flip hopping due to spin-orbit coupling and superconducting pairings in the second coordination sphere are taken into account. The connection between the fermion parity and the parity of the BDI topological invariant is shown. The formation of topological phases with three and four pairs of Majorana modes has been demonstrated.