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- Feb 14, 2012
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Consider the sequence of positive integers which satisfies \(\displaystyle a_n=a_{n-1}^2+a_{n-2}^2+a_{n-3}^2\) for all $n \ge 3$.
Prove that if $a_k=1997$, then $k \le 3$.
Prove that if $a_k=1997$, then $k \le 3$.