令Sn=1*2*3+2*3*4+.+n*(n+1)(n+2)
=1/4[(1*2*3*4-0*1*2*3)+(2*3*4*5-1*2*3*4)+.+
n(n+1)(n+2)(n+3)-(n-1)n(n+1)(n+2)]
=1/4*n(n+1)(n+2)(n+3)
（-1）x（-2）x（-3）+（-2）x（-3）x（-4）+……+（-100）x（-101）x（-102）
=-S100
=-1/4x100x101x102x103=-26527650