Option Explicit
Sub Essai()
Dim Tableau(), X&, dlg&, lig&: Application.ScreenUpdating = 0
dlg = Cells(Rows.Count, "Y").End(3).Row
For lig = dlg To 1 Step -1
With Cells(lig, "Y")
If Trim$(.Value) = "" Then .Value = Tableau(X, 1)
End With
Next lig
End Sub