AoPS Wiki:Problem of the Day/September 3, 2011

Solve for $a_{17}$ if $a_1 + a_2 + a_3 = 1$, $a_2 + a_3 + a_4 = 2, \ldots, a_{16} + a_{17} + a_1 = 16$, and $a_{17} + a_1 + a_2 = 17$.

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