[1] Shahrood Univ Technol, Fac Math Sci, POB 316-36155, Shahrood, Iran
[2] Arak Univ, Fac Sci, Dept Math, Arak 3815688349, Iran
[3] Babes Bolyai Univ, Fac Math & Comp Sci, Cluj Napoca 400084, Romania
[4] Pukyong Natl Univ, Coll Nat Sci, Dept Appl Math, Pusan 608737, South Korea