Parton counting: physical and computational complexity of multi-jet   production at hadron colliders
  We present an enumeration of all possible amplitudes that contribute to an n-jet process in QCD. We estimate the number of amplitudes for large number of jets and determine the actual number of amplitudes to be calculated, which is smaller due to relabelling among (massless) quark flavours. 
Petros D. Draggiotis, Ronald Kleiss