a(n+1)=2an+2^n (两边同除以2^(n+1) )
a(n+1)/2^(n+1)=an/2^n+1/2
a(n+1)/2^(n+1)-an/2^n=1/2
所以an/2^n是以a1/2=1/2为首相d=1/2为公差的等差数列
an/2^n=1/2+(1/2)(n-1)=n/2
所以an=n*2^(n-1)
(n^2)/an=(n^2)/n*2^(n-1)
a(n+1)=2an+2^n (两边同除以2^(n+1) )
a(n+1)/2^(n+1)=an/2^n+1/2
a(n+1)/2^(n+1)-an/2^n=1/2
所以an/2^n是以a1/2=1/2为首相d=1/2为公差的等差数列
an/2^n=1/2+(1/2)(n-1)=n/2
所以an=n*2^(n-1)
(n^2)/an=(n^2)/n*2^(n-1)