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Floor of powers of an irrational equals square minus constant

Source: Brazilian Mathematical Olympiad 2021, Level 3, Problem 3

February 7, 2022
number theoryfloor functionpowersirrational numberPerfect SquaresBrazilian Math OlympiadBrazil

Problem Statement

Find all positive integers kk for which there is an irrational α>1\alpha>1 and a positive integer NN such that αn\left\lfloor\alpha^{n}\right\rfloor is a perfect square minus kk for every integer nn with n>Nn>N.