2207

This number is a prime.

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Largest known prime of the sequence a(0) = 3; thereafter, a(n) = a(n-1)^2 - 2. We start with the prime 3. Then 3^2-2 = 7 is prime. Next 7^2-2 = 47 is prime. Finally, 47^2-2 = 2207 is prime. [Post]