How long does a sequence of random decimal digits (0, 1, 2, ..., 9) need to be before you can "reasonably" expect the sequence to contain all numbers from 0 through 999 (inclusive).
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It's up to you to define "reasonably".
E.g.: The sequence 1823 contains 1, 2, 3, 8, 18, 23, 82, 182 and 823.
The sequence 1053 contains 0, 1, 3, 5, 10, 53, and 105.