[1] Univ Tun Hussein Onn Malaysia, Fac Sci Technol & Human Dev, Dept Math & Stat, Batu Pahat, Johor, Malaysia
[2] Univ Kebangsaan Malaysia, Fac Sci & Technol, Sch Math Sci, Ukm Bangi, Selangor, Malaysia
[3] Univ Babes Bolyai, Dept Math, R-3400 Cluj Napoca, Romania