This number is a composite.
671 is the 3-digit composite number (K) that yields the greatest percentage of primes from Leonhard Euler's formula: X^2 + X + K. 453 out of 1000 possible primes (45.3%). [Morse]
671!/176! + 1 is prime. [Firoozbakht]
(There is one curio for this number that has not yet been approved by an editor.)
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