More than 500,000 books were sold on Amazon’s digital bookstore in October, according to research by The Associated Press and Nielsen BookScan.

That’s the highest number since Nielsen started keeping track in January.

Nielsen said the number of sales on its platform topped 10 million in August, and the total of books sold was up 5 percent from the same month last year.

Readers are also buying more physical books, with more than 11 million copies of The Hunger Games: Catching Fire sold in October.

Amazon’s digital business is growing faster than any other industry in the country, with digital sales topping $1 trillion for the first time in history, according the company.

Amazon has made huge strides in its ability to drive revenue growth and profit in recent years.

The company has seen record revenue growth over the past three years, and it said it has nearly doubled revenue growth since the end of last year, when Amazon surpassed Google to become the largest U.S. digital marketplace.

Amazon said in its third-quarter earnings report that its overall sales were $2.9 billion, up more than $1 billion from the year-earlier period.