Setup text frames on the master page in a new layer above all other layers
Thread the frames in the order you wish the numbers to be applied.
Then on the main pages, import numbers from something like excel where you can easily get 1-400
They should thread to the other frames.
Thanks for the help. So it seems that it is possible to do this but I really could not make any sense from your reply. Can you please elaborate a bit? I'm sorry, I have started using inDesign recently, so do not know a lot of functions.
With a paragraph style with automatic numbering, it is even easier, directly in ID.
Can you please explain how to do it? Thanks.
Create text blocks (chained) on the 2 master pages (1).
Create the paragraph style with the 2 important parameters (2-3). the paragraphs must appear on the master pages.
Go to the current pages and create the number of pages you want.
Chain the last text block of the right page to the first text block of the left page that follows. And so on.
That is all.