IMO Shortlist 1996 problem N1

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Dodao/la: arhiva
2. travnja 2012.
Four integers are marked on a circle. On each step we simultaneously replace each number by the difference between this number and next number on the circle, moving in a clockwise direction; that is, the numbers a,b,c,d are replaced by a-b,b-c,c-d,d-a. Is it possible after 1996 such to have numbers a,b,c,d such the numbers |bc-ad|, |ac - bd|, |ab - cd| are primes?
Izvor: Međunarodna matematička olimpijada, shortlist 1996