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to get the next number in the sequence.
$$57 = 10 \times 5 + 7\quad\quad -6 = 10 \times (-1) + 4 \quad\quad 123 = 10\times 12 + 3$$
This iterative procedure is an example of a dynamical system which can be studied in more detail at university; you may read an introduction to this fascinating subject in Whole Number Dynamics 1 . Dynamical systems using decimals can have many strange and interesting properties; they form the foundation of the subject of chaos, which you can read about on the Plus website .