What was the number one song on January 1 2010?

The number one song on the Billboard Hot 100 chart on January 1, 2010, was "Tik Tok" by Kesha. The song had been at the top of the chart for several weeks, having first reached number one on December 19, 2009. "Tik Tok" was a global hit, reaching number one in several countries around the world and selling over 12 million copies.