The diophantine equation r 2 + r ( x + y ) = k x y . Utz, W.R. — 1985 International Journal of Mathematics and Mathematical Sciences
Positive solutions of the Diophantine equation. Utz, W.R. — 1982 International Journal of Mathematics and Mathematical Sciences
Properties of solutions of the differential equation xx'' - kx'...+ f(x) = 0. W.R. Utz — 1978 Publications de l'Institut Mathématique [Elektronische Ressource]