An=n（n+1)(n+2)=n³+3n²+2nSn=A1+A2+A3+…An=(1³+3×1²+2×1）+（2³+3×2²+2×2）+（3³+3×3²+2×3）+…(n³+3n²+2n)=(1³+2³+3³+…n³﹚＋3×﹙1²＋2²＋3²＋…n²﹚＋2×﹙1＋2＋3＋…n﹚=[n(n+1)/2]²＋3×[n(n+1)(2n+1)]/6 ＋[n﹙n＋1﹚]∕2
