Citation:
Factorial refers to the product of an integer and all the positive integers below it. For example, the factorial of 5 (written as 5!) is equal to 5 x 4 x 3 x 2 x 1.
A recursive function is a function that calls itself within its own definition.
Permutation: Permutation refers to the arrangement of objects in a specific order.
Combination: Combination refers to the selection of objects without considering their order.