Absolutely easy to do, “magical”, clean, portable, can be repeated, and examined, although no reason
for anyone to ask.
You can devine a number, or display the number, or have them repeat the
sequence to get a second number and use the two to predict a card, show the card from a deck, or
magically have the card appear on a tablet after you put it down where the last thing they saw was a
calculator.
This is TV show level for one person or a group. You can get away with it from
any angle.