DataGrid Item auto-generate serial number

when AllowPaging=False

<asp:DataGrid id="DataGrid1" runat="server">
    <Columns>
     <asp:TemplateColumn>
      <ItemTemplate>
       <%# Container.ItemIndex + 1%>
      </ItemTemplate>
     </asp:TemplateColumn>
    </Columns>
 </asp:DataGrid>

or

<asp:DataGrid id="DataGrid1" runat="server">
    <Columns>
     <asp:TemplateColumn>
      <ItemTemplate>
       <%# this.DataGrid1.Items.Count + 1%>
      </ItemTemplate>
     </asp:TemplateColumn>
    </Columns>
 </asp:DataGrid>

AllowPaging="True"

<asp:DataGrid id="DataGrid1" runat="server" AllowPaging="True">
    <Columns>
     <asp:TemplateColumn>
      <ItemTemplate>
       <%# this.DataGrid1.CurrentPageIndex * this.DataGrid1.PageSize + Container.ItemIndex + 1%>
      </ItemTemplate>
     </asp:TemplateColumn>
    </Columns>
</asp:DataGrid>

Reverse order:
//have been defined:
private int RowsCount = ds.Tables[0].Rows.Count

asp:DataGrid id="DataGrid1" runat="server" AllowPaging="True">

                            <Columns>

                                   <asp:TemplateColumn>

                                          <ItemTemplate>

                                                 <%# RowsCount - DataGrid1.CurrentPageIndex * DataGrid1.PageSize - Container.ItemIndex %>

                                          </ItemTemplate>

                                   </asp:TemplateColumn>

                            </Columns>

                     </asp:DataGrid>