The producer of 24 had approached Dan Brown and presented him with an idea of having The Da Vinci Code storyline as the 4th series of 24...he refused wanting it to be a multi-million dollar box office smash. Ron Howard, director of The Da Vinci Code worked as a producer on 24.
Sorry it was 24 creator Joel Surnow who had approach his producer Brian Grazer with the idea but Brown refused and sold the rights to his book to Sony for $6million. Grazer also works as a producer on The Da Vinci Code.