The royal flush is the best hand available in poker. It features five consecutive cards, all of the same suit, in order of value from 10 through to ace. Any five cards of successive values in the same suit that's not a royal flush is a straight flush.

For the counting to 21 game, the winning numbers are 1, 5, 9, 13, 17, and 21 itself. Students should note that we can find these numbers by moving four numbers backwards each time or by repeatedly subtracting four (starting with 21).