Fatto generale: 73 is the length of the Arecibo message sent to space in search for extraterrestrial intelligence.
Fatto matematico: 73 is the smallest multi-digit number which is one less than twice its reverse.
Trivia: 73 is the percentage of girls in Bangladesh that are married by age 18.
Data storica: March 13th is the day in 1964 that American Kitty Genovese is murdered, reportedly in view of neighbors who did nothing to help her, prompting research into the bystander effect.