Prime labeling

Prime labeling --- примитивная разметка, элементарная разметка.

A graph with a vertex set [math]\displaystyle{ V }[/math] is said to have a prime labeling, if its vertices are labelled with distinct integers from [math]\displaystyle{ \{1, 2, \ldots, |V|\} }[/math] such that, for each edge [math]\displaystyle{ xy }[/math], the labels assigned to [math]\displaystyle{ x }[/math] and [math]\displaystyle{ y }[/math] are relatively prime.