Private Sub Worksheet_Change(ByVal Target As Range)
With Target
If .CountLarge > 1 Then Exit Sub
If .Address <> "$C$4" Then Exit Sub
If .Value = "" Then .Offset(, 1).ClearContents: Exit Sub
.Offset(, 1).Formula = "=HYPERLINK(""http://www.crds.fr/jouer/?ref=" & .Value & "&alea=8"")"
End With
End Sub