Markus,

assuming your "numbers" column is in the range A1:A...
then this nasty little routine should sort it out for you.
If you have any problems getting it to run, it may be
because the Usedrange is different from what you think. If
that happens, replace "LastRow" in the "For.." statement
with the number of the last line in your list:

Sub AddRows()

LastRow = ActiveSheet.UsedRange.Rows.Count
For x = LastRow To 2 Step -1

If Cells(x, 1).Value < (Cells(x - 1, 1).Value + 1) Then
Rows(x).Insert
Cells(x, 1).Value = Cells(x + 1, 1).Value - 1
x = x + 1
End If


Next x

End Sub