I have a formula in Excel that looks like this:

```
=VLOOKUP(posts!C12,users!A2:B1800,2)
```

I would like to duplicate this formula down the whole column, however, I would like C12 to increment (C13, C14, C15 etc), but for the rest of the formula to stay the same.

So far, I have tried duplicating it manually onto the next 4 or 5 cells, then selecting those and double clicking the bottom right hand corner of the selection, however this doesn't work, almost, but not quite.