  Theoretical calculations based on the Dirac--Coulomb--Breit relativistic
coupled cluster method have been carried out for the electron affinities and
ionization potentials of the superheavy element nihonium (Nh) and its lighter
homologues In and Tl. The In and Tl calculations are in agreement with
measurement within uncertainties. For Nh, where experiment is yet unknown, we
predict the ionization potential of 7.569(48) eV and electron affinity of
0.776(30) eV.
