Ramanujan-Nagell's Equation and Some of its Variations
  The paper consists of two parts. The aim of the first, and main, part is to explain, in an elementary way, Hasse's proof of Ramanujan-Nagell's Theorem. In the second part, we formulate some natural extensions of Ramanujan-Nagell's equation. 
Boudjem\^aa Anchouche
math.NT