1. Department of Mathematics; Agra College; Agra 282004 Uttar Pradesh India
2. Department of Mathematics; Chaudhary Charan Singh University; Meerut Uttar Pradesh India
3. King Saud University; PO Box 92144 Riyadh 11653 Kingdom of Saudi Arabia
4. School of Computer Science and Engineering; Hunan University of Science and Technology; Xiangtan 411201 China