In a properly laid-out booklet, the sum of the page numbers on any one sheet
will equal one more than the number of pages in the finished booklet, with
the odd page always on the right. The pairs you quote are correct for a
16-page booklet. The idea of "Book fold" is that you can take all the pages
produced (after duplexing), fold them in half, staple in the middle, and
have a working booklet. To this end, page 2 will be on the back of page 1,
but the other end of that sheet will be pages 15 and 16, as follows:

16 and 1
2 and 15
14 and 3
4 and 13
12 and 5
6 and 11
10 and 7
8 and 9