Numbers - formula drag down a cell to increase number by 1

What is the formula to increase a cells number by 1 - in order to make a descending number list from 1 onwards, the way you can do with dates?

In the following snapshot I have tried to grab the yellow dot and copy hoping the next cell will add + 1 .. but all it does is copy the cell?

What is the correct formula to increase the following cell by 1?