Let , and for , let . Find the smallest such that .
Solution
We will show that by induction. Indeed, the claim is obvious for , and . Then we wish to find such that !, or dividing by !, we want . Suppose is composite. Then it has a proper divisor , and since !, we must have , which is impossible. Therefore, must be prime, and if this is the case, then by Wilson's Theorem. Therefore, since the smallest prime greater than 2005 is 2011, the smallest possible value of is 2010.
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