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MathNet 2016-part-07 — 182 problems (EN–VI) Question 46

Math Olympiad Vault · MathNet 2016-part-07 — 182 problems (EN–VI)

Question 46

Call a positive integer $N \geq 2$ "special" if for every $k$ such that $2 \leq k \leq N$, $N$ can be expressed as a sum of $k$ positive integers that are relatively prime to $N$ (although not necessarily relatively prime to each other). How many special integers are there less than $100$?