For "math people": "TRICK" and information in one number

[Siegmund]

The number of possible combinations of m missing cards is 52 choose m. There exist numbering schemes that could, in theory, result in a number between 1 and 52 choose m. Most of them would be fiendishly hard to remember. Ways that give sums between 1 and 52^m would be easier to create.

The trick of remembering two numbers 1-13 and 1-4 runs into trouble with more than one card -- you might be in the position of being able to name two ranks and two suits, but not sure if the two cards are [img]/images/graemlins/heart.gif[/img]7 and [img]/images/graemlins/club.gif[/img]8, or [img]/images/graemlins/club.gif[/img]7 and [img]/images/graemlins/heart.gif[/img]8.

If I were going to do this trick, I would find a prime P>m and a number k<p such that 1^k, 2^k, 3^k, ... (p-1)^k mod p are distinct numbers, and keep track of two or three sums mod P.

If, however, you ask me to identify four or more cards, rather than memorizing four values to associate with every card in the deck (or calculating 37^5 mod 53 in my head!), I will either directly keep track of the 52 cards in my head, or I will start out by remembering 8191,8191,8191,8191, and deducting 2^(rank-1) from the (suit)th number as I go.

I personally would find it easier to learn to count all the cards in the deck than I would to do the subtraction, but non-card-players might find the numbers easier.