Amazon is celebrating the first anniversary of its Android Appstore launch by putting a bunch of its most popular titles on sale. The company revealed that it now sports 31,000 apps on the store, up from 4,000 at launch, and that customers have purchased millions of apps.

Unfortunately, Amazon isn’t being too specific on just how many apps were purchased. The company is historically shy when it comes to granular statistics, like revealing the total number of Kindles it has sold (which we still don’t know). But I have a feeling that, thanks to its daily app deals and promotions, Amazon has done a better job of selling premium apps than Google’s Android Market (now Google Play).

In celebration of its first birthday, Amazon is offering several of its most popular apps for sale, like Plants vs. Zombies, Fruit Ninja, Wolfram Alpha, Splashtop Remote Desktop, Dr. Seuss’s The Shape of Me and Other Stuff, TuneIn Radio Pro, TETRIS, PAC-MAN, The Lost City, MONOPOLY, AccuWeather Platinum, and Jamie Oliver’s 20 Minute Meals.

“We expected that the Amazon Appstore would be a success and it’s been evidenced in the growth of the revenues since the launch,” Adam Flanders, SVP of Sales & Marketing at Glu Mobile, said in a statement today. “We have seen revenues from Amazon grow by over 1,000 percent in the four months since the Kindle Fire launched alone, and Blood and Glory recently reached the #2 spot in Top Selling Games. Glu is thrilled with the momentum behind Kindle Fire and the Amazon Appstore’s strong platform, global customer base, and exceptional merchandising capabilities.”

Amazon also boasted about its Test Drive feature, which lets you try out apps on your computer before you download them to your Android phone or tablet. The company says consumers have spent over 7,700,000 minutes test driving apps, with Bubble Buster being the most-tested. Not surprisingly, Amazon says games were its most popular app category.

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