One of the mysteries of the English language finally explained.
Designating a method of generating a pseudorandom sequence of digits by squaring an arbitrary large number, taking the middle digits of the result (usually half the total number of digits, a zero being added at the left if necessary to make the total even), and using these as the first digits of the sequence and as the number to be squared to provide the next digits, and so on.
1920s (in an earlier sense). From mid + square.
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