1. Lösung der Aufgabe 30;Brauer;Jahresber. Dtsch. Math.-Ver.,1926
2. Algebraic Graph Theory;Godsil,2001
3. On the addition of units and non-units in finite commutative rings;Kiani;Rocky Mountain J. Math.,2015
4. On the addition of units and nonunits mod m;Sander;J. Number Theory,2009
5. Counting solutions of quadratic congruences in several variables revisited;Tóth;J. Integer Seq.,2014