[1+2^(1/2)+3^(1/3)+…+n^(1/n)]/n > [1+1^(1/2)+1^(1/3)+…+1^(1/n)]/n =1
[1+2^(1/2)+3^(1/3)+…+n^(1/n)]/n < [n+n^(1/2)+n^(1/3)+…+n^(1/n)]/n =n^(1/n)
1取极限是1
n^(1/n) 也是1