I knew that artist sometimes made appearances on Sesame Street, but I didn't realize how many!

Check out who's been to Sesame Street:

My favorite by far is when Usher did the ABC Song -- "The ABCs Are Moving You!"

Katy Perry -- You remember that there was controversy about her outfit, but I don't see what the big deal is!

Bruno Mars -- "Don't Give Up"

Jason Mraz singing "Outdoors"...

Common and Colbie Caillat sang "Belly Breathe"

Here's Train's "Five By" with Elmo and the Count

One Direction will be on Sesame Street soon -- here is a preview!