def get_indexes(start_index, chunk_size, nth):
    """
    Creates indexes from a reference index, a chunk size an nth number

    Args:
        start_index (int): first position
        chunk_size (int): Chunk size
        nth (int): The nth number
    
    Returns:
        list: First and last position of indexes
    """
    start_index = nth * chunk_size
    stop_index = chunk_size + nth * chunk_size
    return([start_index,stop_index])