I am wondering how to calculate the number of combinations of $n$ amount of decimal numbers, and $p$ represents amount of numbers chosen out of $n$, where rearrangements are not allowed but duplicates are allowed.
There is a formula that is like this but does not allow duplicates:
$$C(n, r) = \frac{n!}{r!(n - r)!}$$
I am looking for an equation like this but would allow duplicates.