N is the number of items you have. R is the number of places you could put the items. ex. Carlos has 7 paintings, he wants to put 5 of them up in a row. He wants to know how many different combinations of paintings he could have, so he would put 7 for N and 5 for R and get 2520.
This calculator is not made to be used if R is greater than N. Future updates will fix this. I had a little help from the scratch wiki but the rest is me!
