This is a magic trick done using two Arduinos.

One Arduino is a random# generator, the other Arduino will identify a random # chosen by the audience.

Please watch the video. It's easier shown than explained. :-(

Supplies

Any two Arduinos (I used two Arduino Nanos)
Any two or more digit 7-segment display. Sketch is coded for common anode, but it would be simple to modify the sketch for common cathode.
Fourteen 220 ohm resistors
Two momentary push button switches
One numeric keypad
Two breadboards and a handful of jumper wires

Step 1: Build the Randomizer

Wire up the first Arduino as shown in schematic above.

Upload this sketch to this Arduino.

Step 2: Build the Psychic

Wire up the second Arduino as shown in the schematic above.

Upload this sketch to this second Arduino.

Step 3: The Secret

You can build both of the circuits above and they will work together without requiring you to understand how it works.

However, if you learn how it works, you'll be able to use just the Randomizer and guess the random # chosen by your audience, or you could just use the Psychic to have him identify a random#.

This video explains the secret of how the trick works.