Option Explicit
Private Sub Worksheet_Change(ByVal c As Range)
If Not Intersect(c, Range("a3:a65000")) Is Nothing Then
Application.EnableEvents = False
Range("a:a").RemoveDuplicates Columns:=1, Header:=xlYes
Application.EnableEvents = True
Range("a3:a65000").Sort Key1:=Range("a3"), Order1:=xlAscending
End If
End Sub