Easy application to calculate permutations and combinations at once.

✔ Permutation: Selects r sample from n objects, considering the order and not allowing repetition.
✔ Permutation with repetition: Selects r sample from n objects, considering the order and allowing repetition.
✔ Combination: Selects r sample from n objects, not considering the order and not allowing repetition.
✔ Combination with repetition: Selects r sample from n objects, not considering the order and allowing repetition.