数列bn的前n项和为：
Tn=2+2*1+2^2+2*2+……+2^n+2n
=(2+2^2+……+2^n)+(2+2*2+……+2n)
=2(1-2^n)/(1-2)+(2+2n)n/2
=2^(n+1)-2+n(n+1)
=2^(n+1)+n²+n-2