def binomial_prefactor(s,ia,ib,xpa,xpb):
    """
    The integral prefactor containing the binomial coefficients from Augspurger and Dykstra.
    >>> binomial_prefactor(0,0,0,0,0)
    1
    """
    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