1. Zhanjiang Preschool Education College, Zhanjiang 524084, Guangdong, China
2. Foundation Education Institute, Lingnan Normal University, Zhanjiang 524037, Guangdong, China
3. Department of Mathematics, Zhejiang Normal University, Jinhua 321004, Zhejiang, China
4. Department of Mathematics, King Abdulaziz University, Jeddah 21589, Saudi Arabia
5. Department of Mathematics and Statistics, University of South Florida, Tampa, FL 33620, USA
6. School of Mathematics, South China University of Technology, Guangzhou 510640, China
7. College of Mathematics and System Sciences, Shandong University of Science and Technology, Qingdao 266590, Shandong, China
8. School of Mathematical Sciences and Physics, North China Electric Power University, Beijing 102206, China