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Richard Smith watches President Barack Obama deliver his inaugural address during the ceremonial swearing-in, on a television at a Best Buy department store in Springfield, Ill., Monday, Jan. 21, 2013. (AP Photo/Seth Perlman)

NEW YORK (AP) — Nielsen says an estimated 20.6 million people watched President Barack Obama's second inauguration on TV, sharply down from his first inaugural.

The company that measures television audience said that 37.8 million people saw Obama's first inauguration in 2009.

Nielsen said on Wednesday that a total of 18 networks aired some part of this year's inaugural ceremony on Monday.

By The Associated Press