根号1=1
2=1.414
3=1.732
4=2
5=2.236
6=2.449
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