(1)若an=2^n+n-1,求Sn(2)见图

a1=1/2,Sn=n^2an-n(n-1),求Sn和an 已知数列{an}的前n项和为Sn,若a1=1/2,Sn=n^2an-n(n-1)求Sn,an an=(2n-1)*2^(n-1),求Sn an=(2n-1)2^n-1,求sn? an=(2^n+1/(2^n))^2求Sn 已知an=1/2n(n+1),求Sn an=(2n+1)*2^n,求Sn 知Sn=n²+2n+1求an 已知an=(2n+1)*3^n,求Sn An=n×2^(n-1),求Sn an=（2^n-1）n,求Sn 已知:Sn=n平方+2n+1,求An a1=1,Sn=n^2an,求an Sn=2an+(-1)n次方 怎么求an 数列{an}前n项和为sn,若sn/n=3s(n-1)/n-1(n≥2),a1=3,求an an=n(n+1) 求sn an=n*2^n,求Sn an=2^n+n,求Sn