Define a graph $G$ such that $V(G) = \{2,3,4,5,11,12,13,14\}$ and two vertices $s$ and $t$ are adjacent if and only if $\gcd\{s,t\} = 1$. Draw a diagram of $G$ and find its size $e(G)$.
I can understand V(G) = {2,3,4,5,11,12,13,14} but what are "two vertices $s$ and $t$ are adjacent if and only if $\gcd\{s,t\} = 1$"?