1. Department of Mathematics, College of Engineering and Technology, Srinivas University, Mangalore 574146, India
2. Department of Mathematics, Alliance School of Applied Mathematics, Alliance University, Bangalore 562106, India
3. Department of Chemistry, College of Engineering and Technology, Srinivas University, Mangalore 574146, India
4. Department of Mathematics, University of Lome, P.O. Box 1515, Lome, Togo