Values of quadratic forms at primitive integral points. G.A. Margulis, S.G. Dani (1989) Inventiones mathematicae
Variants of the Brocard-Ramanujan equation Omar Kihel, Florian Luca (2008) Journal de Théorie des Nombres de Bordeaux In this paper, we discuss variations on the Brocard-Ramanujan Diophantine equation.