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Sequence of integers and prime numbers

Source: Netherlands IMO Team Selection Test 2013

October 21, 2014
number theoryprime numbersnumber theory unsolved

Problem Statement

Fix a sequence a1,a2,a3a_1,a_2,a_3\ldots of integers satisfying the following condition:for all prime numbers pp and all positive integers kk,we have apk+1=pak3ap+13a_{pk+1}=pa_k-3a_p+13.Determine all possible values of a2013a_{2013}.