答案是n*(n+1)*(n+2)/3
解析如下:=1/3*[1*2*3-0*1*2+2*3*4-1*2*3+3*4*5-2*3*4+...+(n-1)*n*(n+1)-(n-2)*(n-1)*n+n*(n+1)*(n+2)-(n-1)*n*(n+1)]=n*(n+1)*(n+2)/3
答案是n*(n+1)*(n+2)/3
解析如下:=1/3*[1*2*3-0*1*2+2*3*4-1*2*3+3*4*5-2*3*4+...+(n-1)*n*(n+1)-(n-2)*(n-1)*n+n*(n+1)*(n+2)-(n-1)*n*(n+1)]=n*(n+1)*(n+2)/3