def get_frameshift_lengths(num_bins):
    """Simple function that returns the lengths for each frameshift category
    if `num_bins` number of frameshift categories are requested.
    """
    fs_len = []
    i = 1
    tmp_bins = 0
    while(tmp_bins<num_bins):
        if i%3:
            fs_len.append(i)
            tmp_bins += 1
        i += 1
    return fs_len