def get_lhc_sequence_filename_and_bv(beam: int, accel: str = 'lhc'):
    """ Return the default sequence filename, the sequence name and the bv-flag
    for the given beam.

    Args:
        beam (int): beam to use.
        accel (str): accelerator name ('lhc' or 'hllhc').
    """
    as_built = '_as-built' if accel.lower() == 'lhc' else ''
    seq_file = f"lhc{as_built}.seq"
    seq_name = f"lhcb{beam}"
    bv_flag = -1 if beam == 2 else 1
    if beam == 4:
        seq_file = f"lhcb4{as_built}.seq"
        seq_name = f"lhcb2"
    return seq_name, seq_file, bv_flag