This trivia lover’s treasure trove contains the answer to the title question as well as 100 others listed by the numbers from three to twenty four.The authors do not include a list of famous pairs or groups of 16, 17, 19, 21, 22 or 23. The most prolific number sets in this volume are Three and Seven with 19 lists of items each. The authors enumerate 16 categories of Four and 9 groups of Nine. The numbers Six and Twelve contain 8 sections each. Five has 7 sets. Eight and Ten each contain 3 lists. Thirteen and Fifteen have 2 entries. Eleven, Fourteen, Eighteen, Twenty and Twenty-Four each have 1 selection.Art and Music, Religion and Science, History and Literature, Math and Philosophy share the spotlight in this culturally diverse collection of 101 classic sets listed by name and number. Such famous trios as the Musketeers, The Magi and The Fates are listed alongside the Laws of Thermodynamics and Newton’s Laws of Motion. The Four Horsemen of the Apocalypse and the Four Noble Truths of Buddhism are mentioned as well as the Five Pillars of Islam and the Vedas of Hinduism.