Sn=a1+a2+a3+……+an =2^0+2×1-1+2^1+2×2-1+2^3+2×3-1+……+2^(n-1)+2n-1 =[1+2+2^2+2^3+……+2^(n-1)]+2(1+2+3+……+n)-n =(1-2^n)/(1-2)+2×n(1+n)/2-n =2^n-1+n(n+1)-n =2^n+n2-1 给你推荐个学习的网站http://www.jhshuxuefudao.com/