State an equation that best fits these results?

Hi there, this is my first question on here that I am struggling with and would love some clarification:

I needed to do some coin tosses (this has nothing to do with probability) and make a chart based on the tosses and values (starting with 20, each coin toss I would remove all heads up coins and, record what coins are left return all coins that are tails into the cup for the next toss). I would need to repeat this until no coins remain, so here's my results:

toss=coins remaining

0=20

1=15

2=12

3=9

4=5

5=3

6=1

How would I graph these results? I would also need to state an equation that best fits these results? And lastly, I would have to state another equation that would predict the number of remaining coins if I began with N(base=0).

I appreciate all help and thank you for your efforts. (Nod)

I am thinking that the coin tosses =x and the coins remaining after each toss = y? I would need confirmation on this and how to go about doing the equation normally and if I were to begin with N(base=0).