List Type Id for External list
If you are creating and external list via code or CAML and need the type id( the Int32 value for list types) , then the Id for External List is 600.
This corresponds to value used by SPListTemplateType Enumerations. For values of all list types, refer: https://msdn.microsoft.com/en-us/library/microsoft.sharepoint.splisttemplatetype(office.14).aspx