|Look up the INDIRECT() and ROW() functions in Excel Help.|
Combining them should get you what you are asking for.
Put this formula in A2 and drag it down:
In A2, ROW() - 1 will evaluate to 1 so you'll have:
which evaluates to:
As the ROW() function picks up the number of the Row it is in and subtracts 1, it will increment from 1 to 2 to 3 etc.
P.S. I left out the single quote in my formula...put it back in if you really need it.