错项相减-Tn=1+(3×2-1×2)+(5×2^2-3×2^2)+……+(2n-1)2^n-1-(2n-3)×2^n-1)-(2n-1)×2^n=1+2×2+2×2^2+……+2×2^n-1-(2n-1)×2^n=1+2×(2+2^2+……+2^n-1)-(2n-1)×2^n
