21 sales at $4 million and up last week

The dog days of summer took a toll on luxury real estate last week, with just 21 contracts signed on properties $4 million and up, according to Olshan Realty’s latest luxury report.

Of homes that went into contract, the average asking price was $6.8 million; properties spent an average of 350 days on the market.

The top sale of the week was an 11-room penthouse at 240 Riverside Boulevard, asking $15.75 million, down from the asking price of $18.5 million when the apartment first hit the market in March 2012. Measuring 5,168 square feet, the condo has five bedrooms, 4.5 bathrooms, 11-foot ceilings and views of the Hudson River and Central Park.

The No. 2 deal was nearly 10 blocks south at the Alydn at 60 Riverside Boulevard. The four-bedroom, 4.5-bathroom penthouse was asking $9.99 million. With 3,096 square feet, the condo has a six-foot by 15-foot terrace; the building’s 40,000 square feet of amenities include a 75-foot pool, rock-climbing wall, basketball and squash courts, bowling alley and café. [Olshan Realty] – E.B. Solomont