[1] Tianshui Normal Univ, Sch Math & Stat, Tianshui 741001, Peoples R China
[2] King Abdulaziz Univ, Fac Sci, Res Grp, NAAM, Jeddah 21589, Saudi Arabia
[3] Quaid I Azam Univ, Dept Math, Islamabad 45320, Pakistan
[4] Quaid I Azam Univ, Dept Math, Islamabad 44000, Pakistan
[5] Shanghai Univ Finance & Econ, Sch Math, Shanghai 200433, Peoples R China