In the club: Simpson celebrates the milestone in Las Vegas. Plus: Ben & Jen and more

LUCKY NUMBER

Sparks fly – literally – at Ashlee Simpson's 21st-birthday party (complete with a blackjack-themed cake) Sunday at Las Vegas's Pure Nightclub at Caesars Palace. At the bash, she performed a three-song set for an audience that included parents Joe and Tina and big sister Jessica. Her actual birthday is today, Oct. 3.