Prime Labeling of Ladders
  A prime labeling of a graph with $n$ vertices is a labeling of its vertices with distinct integers from $\{1, 2,\ldots , n\}$ in such a way that the labels of any two adjacent vertices are relatively prime. T. Varkey conjectured that ladder graphs have a prime labeling. We prove this conjecture. 
Ebrahim Ghorbani and Sara Kamali
math.CO math.NT