Magic Square Magic Trick

This mental magic trick is an amazing illusion of superhuman memorization and mathematical calculations. It is as close to pure magic as you could ever imagine! It requires no set-up, no special props, no gimmicks, and no accomplices.
There is nothing to hide, no misdirection, and no sleight of hand. The performer can perform the trick at a moment’s notice without any preparation.
It can be performed for one person, a small group, or before a large audience.
Because the performer does the entire trick mentally, there is virtually no way that a spectator can detect exactly how this trick is done.
Although the trick is done mentally, there is a trick. The mental part appears to be very difficult but, because of a trick that only the performer knows, it is actually much, much easier than it appears.