an=1/n求sn=1+1/2+1/3+1/4+...+1/N的通项公式

已知an=(2n+1)*3^n,求Sn an=n(n+1) 求sn 数列{an}前n项和为Sn,且2Sn+1=3an,求an及Sn a1=1/2,Sn=n^2an-n(n-1),求Sn和an 数列an满足a1=1/3,Sn=n(2n-1)an,求an a1=1,Sn=n^2an,求an Sn=2an+(-1)n次方 怎么求an Sn为等比数列{an}前n项和,an=(2n-1)*3的n次方,求Sn 数列an,an=(2n-1)+1/【3n(n+1)】,求Sn An=1/n,求Sn. 数列｛an｝,中,a1=1/3,设Sn为数列｛an｝的前n项和,Sn=n（2n-1）an 求Sn an=(2n-1)*2^(n-1),求Sn an=(2n-1)2^n-1,求sn? 已知an=1/2n(n+1),求Sn an=n+2^（n-1）,求sn an=3/n（n+1）,求sn an=1an=n+2^（n-1）,求sn an=3/n（n+1）,求sn an=1/（2n+1）（2n-1）求sn an=(2^n+1/(2^n))^2求Sn an=(2n+1)*2^n,求Sn 知Sn=n²+2n+1求an