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Number theory Difficulty 5.2 AIME, harder Prove it Ukraine

Find all integer nn, such that:
(n2013)(n2014)(n2016)(n2017)=4. (n-2013)(n-2014)(n-2016)(n-2017)=4.

Solution

If integer number nn satisfies the given condition, then 44 can be presented as product of four pairwise distinct integers. Since the integer divisors of this number are only ±1\pm1, ±2\pm2 and ±4\pm4, we have that sought-for divisors are ±1\pm1 and ±2\pm2. Indeed, if the absolute value of one of divisors is equal to 44 then others are not less than 11 by absolute value, a contradiction. Since n2013n-2013 is the biggest factor, it should be equal to 22. Also we see that n=2015n=2015 satisfies the condition of the problem.

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