LOS ANGELES (SS)KATY Perry is set to sing for President Barack Obama at the 30 Days to Victory concert. The singer will join several artists, who’ve yet to be announced, for the fundraising concert at the Nokia Theatre in LA on October 7. General admission is $250 a person, but supporters under age 40 can purchase a ticket for $44. Katy has always been an avid supporter of the president, who is seeking his second term.