Private Sub Worksheet_Change(ByVal Target As Range)
Dim oRng As Range
    Set oRng = Range("A:A")
    If Target.Cells.Count > 1 Or Target = "" Then Exit Sub
    If Not Intersect(Target, oRng) Is Nothing Then
        If IsNumeric(Target) Then
            On Error Resume Next
            Application.EnableEvents = False
            Target = "BC102014" & CStr(Target)
            Application.EnableEvents = True
            On Error GoTo 0
        Else
            MsgBox "Not a valid number"
            Target.Select
            Target = ""
        End If
    End If
End Sub