12

This number is a composite.

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12 is the largest known even number expressible as the sum of two primes in one way. [Firoozbakht]

12 = (1*2) * (prime(1)*prime(2)). Note that 12 is the only number less than 20000000 with this property. [Firoozbakht]

π(12) = prime(1!) + prime(2!) [Firoozbakht]