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IMO 2016 — Complete Shortlist Question 27

IMO Shortlist · IMO 2016 — Complete Shortlist

Question 27

Define $P(n)=n^{2}+n+1$. For any positive integers $a$ and $b$, the set

$$
\{P(a), P(a+1), P(a+2), \ldots, P(a+b)\}
$$

is said to be fragrant if none of its elements is relatively prime to the product of the other elements. Determine the smallest size of a fragrant set.