1. Department of Mathematics, Paavai Engineering College (Autonomous), Namakkal 637 018, Tamilnadu, India
2. Department of Mathematics, Faculty of Science, University of Hafr Al Batin, P.O. Box 1803, Hafar Al Batin 31991, Saudi Arabia
3. Department of Mathematics and Computer Science, University of Oradea, 1 University Street, 410087 Oradea, Romania
4. Section of Mathematics, International Telematic University Uninettuno, CorsoVittorio Emanuele II, 39, 00186 Roma, Italy