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2021 EGMO P6: floor(m/1) + ... + floor(m/m) = n^2 + a

Source: 2021 EGMO P6

April 13, 2021
EGMO 2021number theoryEGMOasymptoticsalgebraequationcounting

Problem Statement

Does there exist a nonnegative integer aa for which the equation m1+m2+m3++mm=n2+a\left\lfloor\frac{m}{1}\right\rfloor + \left\lfloor\frac{m}{2}\right\rfloor + \left\lfloor\frac{m}{3}\right\rfloor + \cdots + \left\lfloor\frac{m}{m}\right\rfloor = n^2 + a has more than one million different solutions (m,n)(m, n) where mm and nn are positive integers?
The expression x\lfloor x\rfloor denotes the integer part (or floor) of the real number xx. Thus 2=1,π=22/7=3,42=42,\lfloor\sqrt{2}\rfloor = 1, \lfloor\pi\rfloor =\lfloor 22/7 \rfloor = 3, \lfloor 42\rfloor = 42, and 0=0\lfloor 0 \rfloor = 0.