1+2+3+4+.+n,求Sn

1+2+3+4+.+n,求Sn Sn为数列{an}前n项和,(2n-1)Sn+1-(2n+1)Sn=-4n-3 ,求{an}通项公式 Sn=1*2*3+2*3*4+3*4*5+...+n(n+1)(n+2)求Sn 数列求和：Sn=1/1*2*3+1/2*3*4+.+1/n*(n+1)*(n+2) 求Sn 2Sn+Sn-1=3-8/2^n,求Sn 已知数列{an}的前n项和为Sn=1+2+3+4+…+n,求f(n)= Sn /(n+32)Sn+1的最大值f(n)= Sn /(n+32)Sn+1 Sn为分子...(n+32)Sn+1 为分母...看不出来么? an是等差数列,求​lim (Sn+Sn+1)/(Sn+Sn-1)lim (Sn+Sn+1)/(Sn+Sn-1)=[n(n+1)/2+(n+1)(n+2)/2]/[n(n+1)/2+n(n-1)/2]=(2n²+4n+2)/2n²=1+2/n+1/n²我就想知道第一步怎么来的 已知数列前n项和为Sn=1+2+2+3+3+3+4+4+4+4+5+5+5+5+.+n+n+n+n+n+.n,求Sn已知数列前n项和为Sn=1+2+2+3+3+3+4+4+4+4+5+5+5+5+5+......+n+n+n+n+n+......n，求Sn 求数列4,9,16,.,3n-1+2^n,.前n项的和Sn 求Sn=2的n-1次方乘以(4n-3)的n项和 求cn=(3n-2)*(1/4)^n的前n项和Sn Sn=2/2+3/2²+4/2³+····+(n+1)/(2^n) 求Sn. Sn=1+ 4/5 + 7/5² +……+ (3n-2)/5^(n-1)求Sn. 数列bn=2^n(4n-3),求Sn 已知an=(2n+1)*3^n,求Sn 数列{1/（4n^2-1)}的前n项和为Sn,求Sn 设：Sn=1+2+3….n(n∈N),求：f(n)=Sn/(n+32)Sn+1的最大值. 求Sn=1-2+3-4+5-6+```+(-1)^(n+1)*n