Understanding "divides" notation (aka "|") in "d | (k,n)"

Question

I'm wondering what the notation under the sigma symbol means:

I understand that d | k means that d divides k. However, I am unsure of what d | (k,n) means. Does this mean d divides both k and n? Or is there some function (k,n) performed with k and n?

Thank you for the help.

Answer 1

It means $d$ divides the HCF of $k,n$.HCF of $k,n$ is represented by $(k,n)$.

Note-Indirectly it means,$d$ divides both $k$ and $n$.