Solutions of the Exponential Equation 7x^2 + 59y^2 = 3^m. A simple Algorithm producing all the primitive solutions

Abstract

We provide a method, using essentially elementary arithmetic, to solve the exponential diophantine equation 7x^2 + 59y^2 = 3^m, which leads to a simple algorithm, with no use of radicals or complex numbers, that generates all the (infinitely many) primitive and positive solutions of this equation. The method can be generalized to solve a class of exponential equations of the form ax^2 + by^2 = ck^z.