Sixty Million Trillion Combinations is a short mystery story written by Isaac Asimov. It was first published in the May 5, 1980, issue of Ellery Queen's Mystery Magazine, and reprinted in Banquets of the Black Widowers (1984) and The Return of the Black Widowers (2003). Asimov originally entitled it "Fourteen Letters," but the magazine's title was kept in subsequent uses of the story. The story is one of a collection of short mysteries whose characters are based loosely upon the Trap Door Spiders, a stag-club of which Asimov was a member.