For the page numbers, you ordinarily would use a { page } field. Substitute
the following for the even page numbers:

{ = { page }*2 }

To do this, open the header/footer and locate the existing page number.
Select it, and press Ctrl+F9. This will give you:

{ 1 }   (for example... depends on which page you're on at the time)

Modify this to:

{ =1*2 }

Then press F9 to update/collapse the field code. This will give you double
the current page field number.

For the odd numbers, use:

{=1*2-1}