1. Madanpur K. A. Vidyalaya (H.S.), Vill and PO, Madanpur, Nadia 741245, India
2. Department of Pure Mathematics, University of Calcutta, 35 Ballygunge Circular Road, Kol 700019, India
3. Department of Mathematics, Faculty of Sciences, Mazandaran University, P.O. Box 47416-1467, Babolsar, Iran