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IMO 2007 — Complete Shortlist Question 8

IMO Shortlist · IMO 2007 — Complete Shortlist

Question 8

Let $n\gt 1$ be an integer. Find all sequences $a_{1}, a_{2}, \ldots, a_{n^{2}+n}$ satisfying the following conditions:

(a) $a_{i} \in\{0,1\}$ for all $1 \leq i \leq n^{2}+n$;

(b) $a_{i+1}+a_{i+2}+\ldots+a_{i+n}\lt a_{i+n+1}+a_{i+n+2}+\ldots+a_{i+2 n}$ for all $0 \leq i \leq n^{2}-n$.