已知数列{an}中,若a1+2a2+3a3+…+nan=n(n+1)(n+2)则 an=

问题描述:

已知数列{an}中,若a1+2a2+3a3+…+nan=n(n+1)(n+2)则 an=

若a1+2a2+3a3+…+nan=n(n+1)(n+2) (1)
则a1+2a2+3a3+...+(n-1)a(n-1)=(n-1)n(n+1) (2)
nan=n(n+1)(n+2-n+1)
an=3n+3