Two Factorials

Hey Kam, Thanks for reaching out! So, we're introducing factorials because people might not be familiar with the notation. Additionally, we wanted to show what (n+k)! and (n-k)! factorial looks like (where k is just another number like 1, or 4). We also wanted to show what dividing factorials by one another results in, so we displayed n!/k! here.   How about n<k, is there any formula we can use?  Then, we'd just have the same result, as n!/k!, but it would be in the denominator, rather than the numerator.   Also, what is k stand for? We're explaining the algebraic properties of integrals here, so k can be anything we want. In this case, it's just a constant number.   Best, 365 Vik