[1] Univ Putra Malaysia, Fac Sci, Dept Math & Stat, Serdang, Malaysia
[2] Univ Putra Malaysia, Inst Math Res, Serdang, Malaysia
[3] Univ Teknikal Malaysia Melaka, Fak Teknol Kejuruteraan Mekanikal & Pembuatan, Durian Tunggal, Malaysia
[4] Babeş Bolyai Univ, Dept Math, Cluj Napoca, Romania
[5] Acad Romanian Scientists, Bucharest, Romania
[6] Univ Putra Malaysia, Fac Sci, Dept Math & Stat, Serdang 43400, Selangor, Malaysia