[1] Hebei Univ Econ & Business, Sch Math & Stat, Shijiazhuang 050061, Hebei, Peoples R China
[2] Lamar Univ, Dept Math, Beaumont, TX 77705 USA
[3] Alabama A&M Univ, Dept Phys Chem & Math, Normal, AL 35762 USA
[4] King Abdulaziz Univ, Dept Math, Jeddah 21589, Saudi Arabia
[5] Natl Res Nucl Univ, Dept Appl Math, 31 Kashirskoe Shosse, Moscow 115409, Russia
[6] Tshwane Univ Technol, Dept Math & Stat, ZA-0008 Pretoria, South Africa
[7] Univ Witwatersrand, Sch Math, Johannesburg, South Africa