1×2×3+2×3×4+3×4×5+......+n(n+1)(n+2)=1/4【1×2×3×4-0×1×2×3】+1/4【2×3×4×5-1×2×3×4】+1/4【3×4×5×6-2×3×4×5】+......+ 1/4【n(n+1)(n+2)（n+3)-(n-1)n(n+1)(n+2)】=1/4n(n+1)(n+2)(n+3)
