On the representation of numbers in the form of a sum of two squares. (Russian) Zbl 1384.11064
Математическое просвещение. Третья серия. Выпуск 10. Moscow: Moskovskiĭ Tsentr Nepreryvnogo Matematicheskogo Obrazovaniya (MTsNMO) (ISBN 5-94057-227-8). Matematicheskoe Prosveshchenie. Tret’ya Seriya 10, 190-194 (2006).