I am not a big user of Excel but I know I can write 1,2 in two cells and drag my mouse to auto generate rest of numbers.
But somehow it was not working on my Excel 2007 after 10-15 minutes of struggle I was able to fix that.
To fix that click on the office icon on top left and then click on the “Excel Options” then go to “Advance”.
Under “Edit Options” there is a check box named “Enable fill handle and cell drag-and-drop”. Select the check box to enable the auto increment.
Hope this help!!!