Using AutoFill you can fill a column or row of cells with numbers, dates, days of the week, months of the year and other pre-defined data lists.
For example, to fill column G with consecutive numbers starting at 1, type 1 into G4 and 2 into the cell below, select both cells, point your mouse at the little square at the bottom right hand corner of the selected range (the mouse pointer becomes a little black cross) and drag the mouse over the other cells in column G.
However, if you attempt to use AutoFill to fill a column of cells where the cells are on the same rows as filtered data. Excel will copy the value from the first cell and paste it into the other cells in the selected range:
The reason for this is that the cells you are attempting to autofill are not consecutive cells (check out the row numbers on the left hand side)