Assuming that you want this book to have continuous text on the recto
(right-hand) pages and page numbers on both recto and verso pages, the
easiest way to do this is to create two separate files.

1. The first file will consist of pages that are blank except for the page
number.

   a. Create a landscape document with the desired margins and a gutter on
the right equal to half the width of the paper (for Letter, this would be
5.5").

   b. In the header or footer, position the insertion point where you want
the page number, and insert the following field:

       { = { PAGE } * 2 }

       (If you don't know how to create this field, press Ctrl+F9 to insert
the outside pair of field braces. Type "= * 2" (without the quotation marks)
between them, and then click the Insert Page Number button between = and *.)

   c. Press Ctrl+Enter (page break) enough times to create the number of
even pages needed to match the odd pages in the second file.

2. The second file will be your text file.

   a. Create a landscape document with the desired margins and a gutter on
the left equal to half the width of the paper.

   b. In the header or footer, position the insertion point where you want
the page number, and insert the following field:

       { = { PAGE } * 2 - 1 }

   c. Enter the text for your document.

3. When both files are complete, print the text file, then run it back
through the printer to print the "blank" pages.