等差数列{an}的前n项和为Sn,公差d

记数列{an}的前n项和为Sn,若{Sn/an}是公差为d的等差数列,则{an}为等差数列的充要条件是d=? {an}为等差数列,公差d>0,Sn是数列{an}前n项和, 若等差数列{an}的首项为a1,公差为d,前n项的和为Sn,则数列(Sn/n)为等差数列,且通项 等差数列｛an｝前n项和为Sn,且Sn=3n^2+n 求公差d 设公差为d的等差数列{an}的前n项和为Sn,若a1=1,-2/17 已知等差数列{an}的公差d不为零,首项a1=2且前n项和为sn 已知等差数列{an}公差为d(d≠0),前n项和为Sn,Xn表示{an}前n项的平均数,且数列｛Xn｝补充如下： 已知等差数列an的首项a1>0,公差d>0,前n项和为Sn 数列an是公差d不等于0的等差数列,其前n项和为Sn,且 等差数列{an}的前n项和为Sn,且S3=6,a1=4,则公差d等于 设等差数列{an}的前n项和为Sn 已知S3=S12 则当公差d 设等差数列an的公差d为2,前n项和为Sn,则lim(an^2-n^2)/Sn=?