Not a formula that will automatically fill in the rows but you can drag the
formula down but using the fill handle, the little box in the bottom
right-hand corner of the cell.  When you hover the cursor over it, the big
white cross will turn into black crosshairs.  When it does, left-click and
hold as you drag the cursor down the column.

If Column A already has the data fill in then double left-clicking on the
fill handle will fill in the formulas down as fa as the data goes.

Another way is to highlight the column including the first cell with the
formula and select Edit > Fill Down.