# Relatively prime

The number $a$ is relatively prime to $b$ if $a$ has no common factors with $b$, other than 1.

There are lots of ways of expressing this:

• $a$ is prime relative to $b$.
• $a$ is mutually prime to $b$.
• $a$ is coprime to $b$.
• $\mathrm{hcf}(a,b) = 1$.
• $a \perp b$.

For example, 14 and 15 are coprime to each other as $14 = 2 \times 7$, $15 = 3\times 5$—that is, they have no common factors.