the trick is to pick/plant a meaningful large number (8+ digits), then solicit random numbers for use in some arithmetic operations on a phone's calculator app, which astoundingly results in the chosen number despite the random inputs given. of course all the magician does is type the chosen number into the calculator once the irrelevant calculations have been completed and pretends that the number was derived from the calculations.
these 'magicians' might work a little harder at these tricks to at least make them plausible. this one from last week multiplied several natural numbers (and used no other operations). however his chosen number '32771617' is prime and thus couldn't possibly have been derived in this way. disappointing, again.