def weizsaecker(A, Z):
    """
    Calculate the Energy in MeV off a given atom using the Weizsaecker equation
    """
    if A % 2 == 1 and Z % 2 == 1:
        sign = 1
    elif A % 2 == 0 and Z % 2 == 0:
        sign = -1
    else:
        sign = 0
    return ((A - Z) * 939.5445995 + Z * 938.762158 + Z * 0.51099891 - 15.85 *
        A + 18.34 * A ** (2.0 / 3.0) + 92.86 / A * (A * 0.5 - Z) ** 2 + 
        0.75 * Z ** 2 / A ** (1.0 / 3.0) + sign * 35 * A ** (-3.0 / 4.0))
