A^{(1+N)*N/2}=N^2 A^{(1+N)*N}=N^4 (A^N)*(A^n*n)=N^4 lg(A^N)*(A^n*n)=lgN^4 lga^n+lga^(n^2)=4lgN lga^n+2lga^n=4lgN 3lga^n=4lgN lga^n=4/3lgn lga^n=lgn^4/3 结果 a^n=n^(4/3） 即 N 的三分之四方
