On the Diophantine equation \(x^2-Dy^4=1\)
Let \(D\) be a positive integer. In the 1930's, W. Ljunggren gave a necessary and sufficient condition for the equation \(x^2-Dy^4= 1\) to have a positive integer solution \((x,y)\). In this paper the authors give a new and shorter proof of Ljunggren's result.
scientific article; zbMATH DE number 1640504