SerNumberGenerator for PTN

Sub df()
For i = 1 To 2760
a = "XXX3309722015040"
Select Case Len(i)
Case Is = 1:
b = "000"
Case Is = 2:
b = "00"
Case Is = 3:
b = "0"
Case Is = 4:
b = ""
End Select
Cells(i, 1) = a + b + Trim((Str(i)))
Next i
End Sub