1/n(n+2)(n+4)=1/4[1/n(n+2)-1/(n+2)(n+4)]
∴原式=1/4*(1/11*13-1/13*15+1/13*15-1/15*17+……+1/29*31-1/31*33)
=1/4*(1/11*13-1/31*33)
=1/4*(80/13*31*33)
=20/13299