  In this paper, calculated energies of the lowest bound state of Coulomb
three-body systems containing an electron ($e^-$), a negatively charged muon
($\mu^-$) and a nucleus ($N^{Z+}$) of charge number Z are reported. The 3-body
relative wave function in the resulting Schr\"odinger equation is expanded in
the complete set of hyperspherical harmonics (HH). Use of the orthonormality of
HH leads to an infinite set of coupled differential equations (CDE) which are
solved numerically to get the energy E.
