code: def binomial_prefactor(s,ia,ib,xpa,xpb):
      
      total= 0
      for t in range(s+1):
          if s-ia <= t <= ib:
              total +=  binomial(ia,s-t)*binomial(ib,t)* \
                       pow(xpa,ia-s+t)*pow(xpb,ib-t)
      return total
docs: The integral prefactor containing the binomial coefficients from Augspurger and Dykstra.
      >>> binomial_prefactor(0,0,0,0,0)
      1