Pseudorandom number sequence

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A Pseudorandom number sequence is a sequence of numbers that has been computed by some defined arithmetic process but is effectively a random number sequence for the purpose for which it is required.

Although a pseudorandom number sequence in this sense often appears to lack any definite pattern, any pseudorandom number generator with a finite internal state will repeat after a very long sequence of numbers. This can be proved using the pigeonhole principle.

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An other definition :

A set of values or elements that is statistically random, but it is derived from a known starting point and is typically repeated over and over. Pseudo-random numbers provide necessary values for processes that require randomness, such as creating test signals or for synchronizing sending and receiving devices in a spread spectrum transmission. It is called "pseudo" random, because the algorithm can repeat the sequence, and the numbers are thus not entirely random.