1. Department of Mathematics, Laxminarayan Institute of Technology, Nagpur 440033, Maharashtra, India e-mail:
2. Department of Mathematics, Dr. Ambedkar College, Deekshabhoomi, Nagpur 440010, Maharashtra, India e-mail:
3. Department of Mathematics, R.T.M. Nagpur University, Nagpur 440033, Maharashtra, India e-mail:
4. Department of Applied Mathematics, Pillai HOC College of Engineering and Technology, Rasayani 410207, Maharashtra, India; e-mail: