1. Department of Mathematics and Statistics, East Tennessee State University, Johnson City, TN37614-0002, USA;
2. Department of Mathematics, University of Johannesburg, Auckland Park, South Africa;
3. Department of Mathematics, Wingate University, Wingate, NC28174, USA;
4. Professor Emeritus, School of Computing, Clemson University, Clemson, SC29634, USA;
5. Department of Computer Science, Appalachian State University, Boone, NC28608, USA;