A Nordstrom Rack coupon offered in late November 2010 was purchased more than 620,000 times and grossed close to $1 million

After nearly three years of daily deals in an expanding roster of cities all over the world, Groupon has released an astonishing number of coupons. In the process, it has turned itself into a multi-billion-dollar company and spawned a number of copycats on either side of the Atlantic. But what's the all-time best-selling promotion that Groupon has been responsible for since it was founded back in November 2008?

In an infographic created for the Harvard Business Review that takes a close look at the coupon company, data scientist Paul Butler has revealed the most successful Groupon ever. "The runaway hit," according to the infographic, "was a '$25 for $50 at Nordstrom Rack,' offered across the U.S. on November 24, 2010. In San Francisco, that deal grossed so much money -- $857,375 -- that it didn't fit into Butler's chart," which depicts the gross revenue of nearly 950 Groupons offered in San Francisco between June 2009 and February 2011.

"Nationwide some 623,000 people bought the coupon, generating $15.6 million, which accounts for 2.6 percent of cumulative Groupon revenue," the infographic continues.

To put all of this in perspective, the average Groupon sells only 578 units, generating $13,840 at a cost of $34 each. But one of the reasons the Nordstrom Rack deal outperformed every other Groupon is that it was in the sweet spot. Butler's research showed that "coupons that offer $50 worth of merchandise for $25 at retail outlets often perform exceptionally well," which is why we've seen that model repeated time and again.

Image: Groupon.