Copy numbers to fill in blanks

Try this macro

Sub FillInGaps()
Dim Cell As Range
For Each Cell In Selection
    If Cell = "" Then Cell = Cell.Offset(-1, 0)
Next Cell
End Sub

Open up the VBA editor by hitting ALT F11

Insert a new module by hitting Insert - Module

Paste the macro into the empty sheet

Hit ALT F11 to get back to the worksheet.

Run the macro by going to tools-macro in Excel 2003 or the view ribbon in Excel 2007/2010/2013.