But according to city records filed just this week, the real estate developer and Human Rights Watch board member David M. Brown has paid $8.4 million for a three-bedroom Beresford spread (pictured here), which happens to be next door to the three-bedroom co-op he bought for $10.5 million in July 2004. That adds up to $18.9 million, well over four times what Mr. Seinfeld paid just nine years ago.

And 10 floors down, deeds show, hedge fund superstar Vikram Pandit and his wife, Swati, just paid $17.85 million for the late Tony Randall’s 10-room sprawl, with 20 windows facing the park.

Can Mr. Randall’s coffered ceilings, four bedrooms on the park, eight walk-in closets, 21-foot eat-in kitchen and private elevator landing explain the price? “I believed the apartment was worth $17.5, and other people did not,” said listing broker Maria Pashby of the Corcoran Group. “And within two weeks we had a number of families interested.”

Money is funny these days: This year, when Citigroup was rumored to be paying $600 million for Mr. Pandit’s Old Lane hedge fund firm, The Wall Street Journal asked: “[I]s any one person outside of Howard Stern worth that kind of money?” Indeed! The purchase turned out to be closer to $800 million.

Even though Old Lane suffered an embarrassing 5.9 percent drop in August, this month’s Beresford purchase wasn’t hard on Mr. Pandit, though he had to pay over the asking price. “I explained the situation, how much interest we had, and he kindly gave me what we got,” said Ms. Pashby. Never mind that he paid $9.8 million last year for a batch of East 53rd Street condos.

Mr. Brown’s purchase was a tougher choice. “You know something? It’s very hard to buy the house next door,” he said. “When the opportunity presents itself, regardless of how it strangles you, you try to do it. It’s a big deal for us, but I felt you couldn’t walk away.”

He was briefly interested in Mr. Randall’s old place. “He came in with his broker,” according to Ms. Pashby, speaking of Mr. Brown, “and I said, ‘What are you doing here?’ And he said, ‘I need more space.’ And I told him, ‘Go buy the one next door to you.’ And he said, ‘What do you mean the one next door?’”

Incidentally, when a reporter mistakenly phoned up the building’s other David Brown—Helen Gurley Brown’s husband, the Jaws producer—the wrong Mr. Brown was very kind. “There’s another David Brown,” he said. “He gets my mail.”