<image> As shown in the diagram, it is a recursive figure. The width of the spiral passage and the length of OB_{1} are both 1. The spiral line intersects the ray OA at A_{1}, A_{2}, A_{3}, … If the spiral line from point O to point A_{3} is the first loop (with a length of 7), from point A_{3} to point A_{2} is the second loop, from point A_{2} to point A_{3} is the third loop… and so on, the length of the 8th loop is ____.