Natural numbers $a_1,a_2,\dots,a_n$ are called mutually coprime if there is no $p\in\mathbb{N}$ , $p>1$ with $p|a_i$ for all $i\leq n$ . By this definition for example $15$ , $21$ and $25$ would be mutually coprime though they are not pairwise coprime, because that would mean that each pair of these numbers is coprime.