a1=1/2
a2=2+log2(1/2)=1
当n>=2时
a(n+1)-an= (n+2)+log2[(n+1)/(n+2)]- (n+1)-log2(n/n+1)
=1+log2[(n+1)^2/n(n+2)]
=1+log2[(n^2+2n+1)/(n^2+2n)]
>1+log2(1)
=1
所以a(n+1)>an
所以{an}为递增数列
a1=1/2
a2=2+log2(1/2)=1
当n>=2时
a(n+1)-an= (n+2)+log2[(n+1)/(n+2)]- (n+1)-log2(n/n+1)
=1+log2[(n+1)^2/n(n+2)]
=1+log2[(n^2+2n+1)/(n^2+2n)]
>1+log2(1)
=1
所以a(n+1)>an
所以{an}为递增数列