Katy Perry dons a mini dress as she, Lionel Richie and Luke Bryan mark 21 years of American Idol

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Katy Perry was dressed to the nines in a sexy little black mini dress as she celebrated American Idol's anniversary with fellow judges Lionel Richie and Luke Bryan.The California Girls hitmaker, 37, paired her clinging halter-neck frock with knee-high boots.The country crooner, 46, and R&B singer, 73, joined her in more casual looks as the trio marked 21 years of the TV series.

Hot stuff: Katy Perry was dressed to the nines in a sexy little black mini dress as she celebrated American Idol's anniversary with fellow judges Lionel Richie and Luke BryanFlocking to New Orleans for the special occasion, the three powerhouse entertainers were met by a crowd of supporters.They each held up small plaques that read 'you're invited' as they began the latest season of the music competition show.

Perry, who burst onto the music scene in the early aughts with her cheeky hit I Kissed A Girl, wore her dark hair in a sleek updo.She left long, face-framing curtain bangs out in the front that were separated by an abbreviated center part.

Celebration: The country crooner, 46, and R&B singer, 73, joined Katy in more casual looks as the trio marked 21 years of the TV seriesWalking a red carpet on her right side was Luke, who was dressed in double denim with a button-up shirt, jeans, and cowboy boots.Lionel, who's father to Hollywood starlets Nicole and Sofia Richie, wore a mostly black outfit.The Hello singer-songwriter added a burnt orange jacket over the dark look, leaving it unzipped.The three personalities were equally hyped up for the event in which they announced who was invited to the Hollywood Show.