1. Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
2. Faculty of Mathematics and Statistics, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
3. Department of Mathematics, Faculty of Sciences, Gazi University, Ankara, Turkey;
4. Faculty of Basic Sciences, Vinh Long University of Technology Education, Vinh Long, Vietnam