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Number theory Difficulty 4.8 AIME Prove it Mongolia

If mm and nn are positive integers, can the number m4+2mn+n22021m^4 + 2mn + n^2 - 2021 be the product of three or more consecutive integers?

Solution

Answer: No.
Suppose that N=m4+2mn+n22021N = m^4 + 2mn + n^2 - 2021 is the product of three or more consecutive integers. Then NN and m4m2=m[(m1)m(m+1)]m^4 - m^2 = m[(m-1)m(m+1)] are divisible by 33. Thus (m+n)2N(m4m2)+20212(mod3)(m+n)^2 \equiv N - (m^4 - m^2) + 2021 \equiv 2 \pmod{3}, which is a contradiction, since 22 is not a quadratic residue modulo 33.

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