a1=A an+1=Sn+(-1)^n,且 an+2/3[(-1)^n ]是等比数列,(1)求A的值,(2)求通项公式an(3)求证1/a3+1/a4+.+1a1=A an+1=Sn+(-1)^n,且 an+2/3[(-1)^n ]是等比数列,(1)求A的值,(2)求通项公式an(3）求证1/a3+1/a4+.+1/a2n 小于3/2

数列{An},A1=1,A(n+1)=3An+4.求An和Sn. a1=1,Sn=n^2an,求an 已知数列 an前n项和为Sn,a1=1,Sn=2a(n+1),求Sn a1=1/2,Sn=n^2an-n(n-1),求Sn和an 已知数列｛an｝满足a1=1,a（n+1）=sn+（n+1）求：an和sn an=a1+(n-1)d 和Sn=n(a1+an)/2中an是什么意思? an=a1+(n-1)d 和Sn=n(a1+an)/2中an是什么 等比数列{an},Sn=2^n-1,则a1^2+a2^2+...+a^n=? 等差数列前n项和为Sn,若a（n+1）=3Sn,a1=1,则通项an? 设数列{an}的前n项和为Sn,a1=10,a(n+1)=9Sn+10 在等差数列an中.a1=1,Sn=a1+a2+...+an,求lim(1+Sn)/(n(1-a(n+1))),d不等于0 A1=1,且An=Sn/n+a(n-1).a是常数.证明An是等差数列 在数列{an}中,a1=2,sn=4A(n+1) +1 ,n属于N*.求数列{an}的前n项和Sn 数列an满足a1=1/3,Sn=n(2n-1)an,求an a1=1,an+1=an+3^n-n,求an与sn a1=1/2,an+1=an/an+2,求n/an的sn a1=1,n,an,Sn成等差数列,证明｛Sn+n+2}是等比数列 数列{an}的前n项和为Sn,若a1=1,Sn=3a n+1 ,则Sn等于:n+1是脚标