Are there any variations on the 21 card trick out there. There is a simple mathematical formula for figuring out how many cards can be used, and how many times a spectator has to choose the row his card is in (and of course, how many rows are available for the spectator to choose from).
I'm working on an effect where the spectator shuffles the deck, deals out five poker hands (face down), picks up a hand, looks at it and chooses a card from his hand. Etc. Etc.
Someone in the forum mentioned this trick, and it got me thinking about how the original 21 trick is pretty amazing to someone who's never seen it before.
EDIT: I came across a similar handling in a Martin Gardner book. I'm disappointed in his explaination of the mechanics.
