There is nothing wrong with this book. Because (6n+5)/ 12 is an "accumulation method" in which the item 1 is subtracted from the item 2, the item 2 is subtracted from the item 3, and the item 4 is subtracted from the item 3 until the item n is subtracted from the item n- 1, so the accumulation method in this question starts from the item 2, that is, n=2. So it is necessary to verify n= 1 generation (6n+5)/ 12. Upon verification, n= 1 cannot be included. Therefore, the items 1, 47/ 12(n= 1) should be added.