A divisibility problem
Under what circumstances is/isn’t C(n,r) divisible by n?
Assume that n and are r integers (include 0 and negatives).
C(n,r) = n! / ((n-r)! r!)
You might find it convenient to use e.g. a|b for “a divides b”
and a¦b for “a doesn’t divide b”
On my British keyboard, the | is next to the Z and
the ¦ is next to the top left 1 and is accessed with the Alt Gr key