1. On a restricted linear congruence;Bibak;Int. J. Number Theory,2016
2. Restricted linear congruences;Bibak;J. Number Theory,2017
3. Lösung der Aufgabe 30;Brauer;Jber. Deutsch. Math.-Verein,1926
4. An extension of Ramanujan's sum;Cohen;Duke Math. J.,1949