1. Department of Mathematics, Federal Institute of Science and Technology, Angamaly 683577, Kerala, India
2. Department of Mathematics, St. Xavier’s College for Women, Aluva 683101, Kerala, India
3. National Centre for Advanced Research in Discrete Mathematics, Kalasalingam Academy of Research and Education, Anand Nagar, Krishnankoil 626126, Tamil Nadu, India
4. Department of Mathematics, Amrita Vishwa Vidyapeetham, Coimbatore 641112, Tamil Nadu, India
5. Department of Computer Science, Ball State University, Muncie, IN 47306, U.S.A
6. Department of Computer Science, Liverpool Hope University, Liverpool, U.K