Number theoryDifficulty 4.8AIMEProve itSaudi Arabia
Prove that 2014 divides 53n55−57n53+4n for all integer n.
Solution
Notice first that 2014=2×19×53. Applying Fermat's little theorem for the prime numbers 2,19,53 we obtain: 53n55−57n53+4n≡n−n+0≡0mod253n55−57n53+4n≡15n17(n19)2−0+4n≡15n19+4n≡19n≡0mod19and 53n55−57n53+4n≡0−4n+4n≡0mod53 for all integer n. Therefore 2014 divides 53n55−57n53+4n for all integer n.
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Source: MathNet,
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