13. A traveler returned to the hotel. This time he had a chain with 7 links. He had to pay one link per day for his stay, but the hotel owner warned that he would accept no more than one cut link. Which links should be cut so that the traveler can stay in the hotel for 7 days and pay the owner daily?
13. The third link should be cut. This will cause the chain to break into pieces consisting of one, two, and four links. On the first day, he should give one link, on the second day, two links, receiving one back in change, on the third day, one link again, on the fourth day, four links, and receive back the pieces of one and two links, and then repeat the operations of the first three days.