1. Department of Mathematics, College of Science, Bengbu University, Bengbu Anhui 233000, People’s Republic of China.
2. School of Mathematical Sciences, Yangzhou University, Yangzhou 225002, People’s Republic of China
3. Sichuan Vocational and Technical College, Suining 629000, People’s Republic of China.
4. School of Mathematics and Information, China West Normal University, Nanchong 637009, People’s Republic of China.