The Number Ones: Katy Perry's “California Gurls” (Feat. Snoop Dogg)

American Idol: All Of Katy Perry's #1 Songs On The Billboard Charts

Teenage Dream, album by Perry

Shakira - Hips Don't Lie ft. Wyclef John *2006* (her only no.1 song in the Billboard Hot 100) : r/Xennials

Britney Spears - Blackout era : r/popculturechat

Katy Perry - California Gurls

BBC - Chart Blog: Katy Perry and Snoop Dogg - 'California Gurls

California Gurls chords by Katy Perry/Snoop Dogg - Spy Tunes

Lee Hazlewood and Nancy Sinatra 1968. The same year they released their first collaborative album. : r/OldSchoolCool

The Number Ones: Katy Perry's “Firework” : r/popheads

Celebrating 10 Years of Katy Perry's History-Making Pop Era

The Week in Number Ones: Dr. Dre, Ed Sheeran and Van Halen