The term 'twenty-one' can be represented in a variety of ways. The nine-letter solution 'BLACKJACK' refers to the popular card game, also known as 21. The three-letter solution 'XXI' is the Roman numeral for 21. The ten-letter solution 'tvgameshow' is a reference to the long-running American game show 'Twenty-One', which aired from 1956 to 1958. The fifteen-letter solutions 'fiveplussixteen', 'seventimesthree', 'sixteenplusfive', 'thirtyminusnine', and 'twointofortytwo' are all mathematical equations that equal 21.