1/√2 1/√3 1/√10 1/√15 1/√26 1/√35 1/√50(答案)
实际就是2,3,10,15,26,35,...规律
1 2 n^2+1
2 3 n^2-1
3 10 n^2+1
4 15 n^2-1
5 26 n^2+1
6 35 n^2-1
7 50 n^2+1