1. Department of Mathematics and Statistics, College of Science, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia
2. Department of Mathematics, Faculty of Science, Federal University Dutse, Dutse P.O. Box 7156, Jigawa State, Nigeria
3. Center for Applied Mathematics and Bioinformatics (CAMB), Gulf University for Science and Technology, Hawally 32093, Kuwait
4. Department of Mathematics, University of Illinois, Urbana Champaign, Urbana, IL 61801, USA