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For a generator of ''n''-digit numbers, the period can be no longer than 8<sup>''n''</sup>. If the middle 4 digits are all zeroes, the generator then outputs zeroes forever. If the first half of a number in the sequence is zeroes, the subsequent numbers will be decreasing to zero. While these runs of zero are easy to detect, they occur too frequently for this method to be of practical use. The middle-squared method can also get stuck on a number other than zero. For ''n''=4, this occurs with the values 0100, 2500, 3792, and 7600. Other seed values form very short repeating cycles, e.g., 0540-2916-5030-3009. These phenomena are even more obvious when ''n''=2, as none of the 100 possible seeds generates more than 14 iterations without reverting to 0, 10, 60, or a 24-57 loop.
In the 1949 talk, Von Neumann famously quipped that, "Any one who considers arithmetical methods of producing random digits is, of course, in a state of [[sin]]." What he meant, he elaborated, was that there were no true "random numbers," just means to produce them, and "a strict arithmetic procedure," like the one described above, "is not such a method." Nevertheless he found these kinds of methods much quicker (hundreds of times faster) than reading "truly" random numbers off [[punch cards]], which had practical importance for his [[ENIAC]] work. He found the "destruction" of middle-square sequences to be a factor in their favor, because it could be easily detected: "one always fears the appearance of undetected short cycles."<ref name="vonneumann"
==References==
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