Private Sub Worksheet_Change(ByVal Target As Range)
Dim c As Range, amount As Long
Dim RngTo As Range, RngIs As Range
If Intersect(Range("N3:N400"), Target) Is Nothing _
Or Not IsNumeric(Target.Value) Then Exit Sub
On Error GoTo fail
amount = Round(Target.Value - 1, 0)
Set RngIs = Target.Offset(, -7)
Set RngTo = Target.Offset(1, -7).Resize(amount)
For Each c In RngTo.Cells
If c.Value <> "" And c.Value <> RngIs.Value Then Err.Raise 501
Next c
Application.EnableEvents = False
RngTo.Value = RngIs.Value
Application.EnableEvents = True
On Error GoTo 0
fail:
If Err.Number Then MsgBox Target.Value & " forbidden"
End Sub