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APMO 2017 - Asian Pacific Mathematics Olympiad Question 5

APMO · APMO 2017 - Asian Pacific Mathematics Olympiad

Question 5

Let $n$ be a positive integer. Call two integer $n$-tuples $(a_1,\ldots,a_n)$ and $(b_1,\ldots,b_n)$ an exquisite pair if
$$|a_1b_1+\cdots+a_nb_n|\le1.$$
Determine the maximum number of distinct integer $n$-tuples such that every two distinct members form an exquisite pair.

Proposed by Pakawut Jiradilok and Warut Suksompong, Thailand.