1Department of Mathematics and Statistics, Western Michigan University, Kalamazoo, MI 49008, USA, e-mail: chartrand@wmich.edu2Engineering, Mathematics and Physical Sciences Division, Modesto Junior College, Modesto, CA 95350, USA, e-mail: enya505@aol.com3Department of Mathematics and Computer Science, University of Detroit Mercy, Detroid, MI 48219, USA, e-mail: drsaba@hotmail.com4Department of Mathematics Sciences, University of Nevada, Las Vegas, Las Vegas, NV 89154, USA, e-mail: salehi@nevada.edu5Department of Mathematics and Statistics, Western Michigan University, Kalamazoo, MI 49008, USA, e-mail: zhang@math–stat.wmich.edu