1. The diophantine equation 2n=x2+7
2. All integer solutions of 2n-7=x2 are given by w = 3, 4, 5, 7, 15, Kongl. Norske Vidensk. Selsk;Chowla-M;Forhandl. (Trondheim) B,1960
3. On the equation 2n-D=y2;Schinzel;Bull, Acad. Pol. Sci.,1960
4. Linear recurrences of order two