The mininima of positive definite Heranmitian binary quadratic forms A. Oppenheim — 1934 Mathematische Zeitschrift
The representation of real numbers by infinite series of rationals A. Oppenheim — 1972 Acta Arithmetica
The rational integral solution of the equation a(x³+y³)=b(u³+v³) and allied Diophantine equations A. Oppenheim — 1964 Acta Arithmetica