OA2? + A2A3? = OA3?
So OA 1? + A 1A2? + A2A3? = OA3?
OA3? + A3A4? = OA4?
So OA 1? + A 1A2? + A2A3? + A3A4? = OA4?
So OA 1? + A 1A2? +...........+ An- 1An = OAn?
OA 1 = a 1 a2 = a2 a3 = a3 a4 =…= A8 a9 = 1。
So N = OAn?
N=25
24 numbers from 2 to 25.
* * * A rational number with four numbers: 4,9,16,25.
So the length of 20 line segments is unreasonable.