In ESP testing, some experiments involve having a list of random numbers for a subject to guess. Often, such a list is developed on a computer. However, it’s difficult to progam for randomness, so usually the computer is given a complex mathematical calculation that results in a seemingly endless set of digits that do not have a pattern. Even though this is based on a formula and not truly random, such pseudo-random numbers, for all practical purposes, are unpredictable and effectively simulate a list of random numbers.