Jordan's totient function

In number theory, Jordan's totient function, denoted as ${\displaystyle J_{k}(n)}$, where ${\displaystyle k}$ is a positive integer, is a function of a positive integer, ${\displaystyle n}$, that equals the number of ${\displaystyle k}$-tuples of positive integers that are less than or equal to ${\displaystyle n}$ and that together with ${\displaystyle n}$ form a coprime set of ${\displaystyle k+1}$ integers

Jordan's totient function is a generalization of Euler's totient function, which is the same as ${\displaystyle J_{1}(n)}$. The function is named after Camille Jordan.