IMO Shortlist 2005 problem N1
Dodao/la:
arhiva2. travnja 2012. Determine all positive integers relatively prime to all the terms of the infinite sequence
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Determine all positive integers relatively prime to all the terms of the infinite sequence $$a_n=2^n+3^n+6^n -1,\ n\geq 1.$$
Izvor: Međunarodna matematička olimpijada, shortlist 2005