If $a$ is a root of $x^3-x-1 = 0$, compute the value of $$a^{10 }+ 2a^8 -a^7 - 3a^6 - 3a^5 + 4a^4 + 2a^3 - 4a^4 - 6a - 17.$$


Let's think step by step and output the final answer within \boxed{}.
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