Numb3rs - Season 1 Episode 5
Prime Suspect

When a five-year-old girl is kidnapped from her birthday party, Don and Terry lead the investigation, but must rely on Charlies help because the girls father, Ethan, is also a mathematician. Charlie realizes the kidnappers motive when Ethan reveals he is close to solving Riemanns Hypothesis, a difficult math problem. If solved, the solution could not only earn him $1 million, but could break the code for internet security and unlock the worlds biggest financial secret.