Permutation Coefficient What is Permutation Coefficient
Permutation refers to the process of arranging all the members of a given set to form a sequence. The number of permutations on a set of n elements is given by n! , where “!” represents factorial.
The Permutation Coefficient represented by P(n, k) is used to represent the number of ways to obtain an ordered subset having k elements from a set of n elements.
Mathematically,

Examples:
P(10, 2) = 90
P(10, 3) = 720
P(10, 0) = 1
P(10, 1) = 10

To Calculate the Permutation Coefficient, you can use the following recursive approach:
P(n, k) = P(n-1, k) + k * P(n-1, k-1)
Though, this approach can be slow at times. So Dynamic approach is preferred mostly.
Example of Dynamic Approach (Python)
Input Format
{n} {k}
Output Format
{PermutationCoefficient}
Test Cases
INPUT - 100 2
OUTPUT - 9900

INPUT - 69 5
OUTPUT - 1348621560

INPUT - 20 19
OUTPUT - 2432902008176640000

INPUT - 15 11
OUTPUT - 54486432000

Constraints in input
N will always be greater than or equal to K.
(Not to be confused with Binomial Coefficient)
APL (Dyalog Extended), 5 bytes

⊣÷⍥!-

⊣      left argument
 ÷⍥!   divide over factorial, apply factorial to both arguments and then divide
    -  subtract

Try it online!