1.1
2.1.414
3.1.732
4.2
5.2.236
6.2.450
7.2.646
8.2.828
9.3
10.3.162
11.3.317
12.3.464
13.3.606
14.3.742
15.3.873
16.4
17.4.123
18.4.243
19.4.359
20.4.472
这是近似值,要再精确就用计算器吧.