Ever wonder why we ask that the number of pages in your layout be divisible by four?
It has to do with the bindery method that you have chosen. If you are printing a piece that is saddle stitched you need to have a page count based on four pages to fill the spread count. Each spread is made up of four pages.
With a saddle-stitch book we can’t have missing pages, pages can be blank, but they must be in your layout. Acceptable layout page counts are: 4, 8, 12, 16, 20, 24, 28, etc.
Other Bindery methods require page counts be divisible by 2: Wire-O, GBC, Perfect Binding, Tape. Except that sometimes it can be more cost effective to have your page count divisible by 4. It all has to do with how the pages get printed and how the bindery work is engineered.
Divide by 2 or 4, but before you get too far with the math, give your salesperson or CSR a call and check on the engineering for your job. They might have some good suggestions for you to keep your costs down and the quality up. And they can tell you what the best page count is for your project.