1. School of Mathematics and Statistics, Hanshan Normal University, Chaozhou, Guangdong 521041, China
2. Faculty of Information Technology, Macau University of Science and Technology, Macau, China
3. School of Mathematics and Statistics, Zhaotong University, Zhaotong, Yunnan 657000, China
4. Faculty of Science, University of Kragujevac, Radoja Domanovica 12, 34000 Kragujevac, Serbia
5. Faculty of Mechanical Engineering, University of Belgrade, Kraljice Marije 16, 11120 Belgrade, Serbia