Number theoryDifficulty 5.1AIME, harderProve itPhilippines
Problem: Let N=20192−1. How many positive factors of N2 do not divide N?
Solution
Solution: Note that N=23⋅5⋅101⋅1009 and so N has 4⋅2⋅2⋅2=32 factors. On the other hand, N2=26⋅52⋅1012⋅10092 and so N2 has 7⋅3⋅3⋅3=189 factors. Hence, 189−32=157 of these factors of N2 do not divide N.
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