alex and sierra x factor

Alex & Sierra perform on "The X Factor." The duo's cover of "Gravity" was No. 1 on iTunes' song chart (Ray Mickshaw / Fox / November 27, 2013)

It may not be having the best season in the ratings, but Simon Cowell's "X Factor" is definitely a factor in song sales. 

The sweetheart duo Alex & Sierra's cover of the Sara Bareilles song "Gravity" has the top spot on iTunes' song chart following their performance on the Fox show this week. Their version of A Great Big World's "Say Something" was also still in the top 10 as of Friday afternoon after hitting No. 1 last week. 

Alex & Sierra, who are dating, are not the only "X Factor" finalists performing well on the charts.

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Jeff Gutt's performance of the frequently covered Leonard Cohen-penned "Hallelujah" is in the top 10 overall, while on the rock chart, he has six of the top 10 singles. Carlito Olivero has the No. 6 song on iTunes' Latin chart. 

TV programming is a powerful driver of digital singles, with shows such as NBC's "The Voice" and Fox's "Glee" often producing tracks that climb the iTunes rankings. In fact, A Great Big World and Christina Aguilera's recording of "Say Something" is still a top seller on iTunes, helped by their performance on "The Voice," on which Aguilera is a judge. 

In terms of TV ratings, "The Voice" far outpaces the "X Factor," with the former routinely pulling in more than twice as many viewers. Both series air season finales next week.    

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While "X Factor," now in its third season in the U.S., is generally down in the ratings from last year, the franchise does have a track record of launching pop music careers, with One Direction, Fifth Harmony and Emblem3 as prominent examples.

One Direction, the boy band assembled during the British version of the show in 2010, has sold 35 million records worldwide.

Both Fifth Harmony and Emblem3 came out of the American version's 2012 season. 

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ryan.faughnder@latimes.com