31 (Thirty-One, French Trente-et-un) is one of the oldest known card games. It is already mentioned in a French translation of a 1440 sermon by the Italian preacher Bernardino of Siena and may be Italian. The game spread across Europe and was recorded in England by Francis Willughby in the 1670s. The old Trente-et-un is seen as a forerunner of Vingt-et-un and so of blackjack. The modern three-card version with knocking is also called Scat and Blitz. Its German relative Schwimmen is played with 32 cards.
Sources: Thirty-one · Schwimmen