｛（k＋1）！｝＾2−(k＋1)＾k＋1＝(k!)＾2（k＋1）＾2−（k＋1）＾k＋1＞k＾k（k＋1）＾2−（k＋1）＾k＋1＝k＾k−1（k＋1）＾2｛k−（1＋1／k）＾k−1｝