an=n+2^(n-1),求sn an=3/n(n+1),求sn an=1
an=(2^n-1)n,求Sn
已知an=(2n+1)*3^n,求Sn
Sn+an=(n-1)/n(n+1),求an
已知a1=3,an=Sn-1+2^n(n大于等于2),求an,Sn?
已知an=1/2n(n+1),求Sn
An=n×2^(n-1),求Sn
已知an=5n(n+1)(n+2)(n+3),求数列{an}的前n项和Sn
已知数列an前n项和为Sn,且满足4(n+1)(Sn+1)=(n+2)^2an(n属于正整数) 求an
已知数列{an}中,an=(2n+1)3n,求数列的前n项和Sn
等比数列an的前n项和为sn,sn=1+3an,求:an
数列{an}前n项和为Sn,且2Sn+1=3an,求an及Sn
在数列{an}中,an=1/n(n+1)(n+2),求Sn的极限