I suggest you may not want to use Autonumber for that use. Autonumbers are
designed to provide unique numbers. It in not designed to provide numbers
in order and for a number of reasons may not do so. As a result using them
in any application where the user sees the numbers is likely to end up with
confusion.
There are other ways of providing the numbers you want depending on the
particual application.
There is at least one way to do what you want, but I suspect someone
else will have a better way than I do, so I will not suggest it yet.