1. University of Priština in Kosovska Mitrovica, Faculty of Sciences and Mathematics, Department of Mathematics, Lole Ribara 29, 38220 Kosovska Mitrovica, Serbia.
2. University of Niš, Faculty of Agriculture in Kruševac, Kosančićeva 4, 37000 Kruševac, Serbia.
3. Mathematical Institute of Serbian Academy of Sciences and Arts, University of Belgrade, Knez Mihaila 36, 11000 Beograd, Serbia.
4. University of Niš, Faculty of Sciences and Mathematics, Department of Mathematics, Višegradska 33, 18000 Niš, Serbia.