def abc_q2d(n, m):
    """A, B, C terms for 2D-Q polynomials.  oe-20-3-2483 Eq. (A.3).

    Parameters
    ----------
    n : int
        radial order
    m : int
        azimuthal order

    Returns
    -------
    float, float, float
        A, B, C

    """
    # D is used everywhere
    D = (4 * n ** 2 - 1) * (m + n - 2) * (m + 2 * n - 3)

    # A
    term1 = (2 * n - 1) * (m + 2 * n - 2)
    term2 = (4 * n * (m + n - 2) + (m - 3) * (2 * m - 1))
    A = (term1 * term2) / D

    # B
    num = -2 * (2 * n - 1) * (m + 2 * n - 3) * (m + 2 * n - 2) * (m + 2 * n - 1)
    B = num / D

    # C
    num = n * (2 * n - 3) * (m + 2 * n - 1) * (2 * m + 2 * n - 3)
    C = num / D

    return A, B, C