An=(2n+1)^2/[2n(n+1)]
An=(4n^2+4n+1)/2n(n+1)=2+1/2n(n+1)=2+1/2(1/n-1/n+1)
Tn=2n+1/2(1-1/n+1)
Tn=2n+n/(2n+2)