数列｛an｝满足a1＋2a2＋3a3＋…＋n（n＋1）（n＋2）,求数列｛an｝的通项公式.

已知数列{an}满足a1＝1,an=a1＋1/2a2＋1/3a3+…＋1/(n－1)an 已知等比数列{an}满足2a1＋a3＝3a2.且a3+2是a2.a4的等差中项.求数列已知等比数列{an}满足2a1＋a3＝3a2.且a3+2是a2.a4的等差中项. 求数列{an}的通项公式 设数列{an}的前n项和为sn,求S15 已知数列{an}满足a1+2a2+3a3+…+nan=n(n+1)(n+2),则a1+a2+a3+…+an=多少? 数列{an}满足:a1,a2-a1,a3-a2……,an-an-1构成以2为首项,3为公比的等比数列,求an 设数列{An}满足a1＝1.Sn＝a1＋a2＋a3＋…＋an＝n2 （1）当n>=2时.求Sn-Sn-1（2）求数列的通项公式An 数列｛an｝满足a1＋2a2＋3a3＋…＋n（n＋1）（n＋2）,求数列｛an｝的通项公式. 数列an满足a1=1/2,a1+a2+a3……an=n^2an,则an 设数列﹛an﹜满足a1＝1／2,a1＋a2＋a3＋…＋an＝n²an,用数学归纳法证明an＝1／[n﹙n＋1﹚] 已知数列an满足a1+2a2+3a3+……+nan=2^n,求an 错位相减法求和设数列满足a1＋3a2＋3∧（2)×a3…3^(n-1)an=n/31.求an通项2.设bn=n/an 求bn前n项和 已知数列{an}满足a1=1,an=a1+2a2+3a3+……+(n-1)an-1 (n≥2)求an=? 设数列{an}满足：a1+a2/2+a3/3+a4/4……+an/n=An+B,其中A、B为常数.数列{an}是否为等差数列? 已知数列{an}为等比数列a1＋a2+a3=21 a1×a2×a3＝216 求an (1)数列{an}中,a1=1,a2=-3,a(n+1)=an+a(n+2),则a2005=____(2)已知数列｛an｝满足a1=1,a1×a2×a3…an=n^2,求an. 数列{an}满足a1＝1／2,a1＋a2＋……＋an＝n的平方×an,则数列{an}的通项公式? 数列an满足a1=1,a2=2,an+2=(1-1/3cos^2n*π/2)+2sin^2*π/2,（1）求a3、a4及数列an的通项公式（2）设S...数列an满足a1=1,a2=2,an+2=(1-1/3cos^2n*π/2)+2sin^2*π/2,（1）求a3、a4及数列an的通项公式（2）设Sn＝a1＋a2＋… 数列{an}满足:a1+3a2+5a3+…+(2n-1)an=(n-1)3^n+1+3,则数列{an}的通项公式为 数列{an}满足:a1+3a2+5a3+…+(2n-1)an=(n-1)3^n+1+3,则数列{an}的通项公式为