5

This number is a prime.

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All the solutions of n = π(2n) are nonnegative integers less than 5. [Firoozbakht]

For the first five primes we have prime(2)*prime(4) - prime(1)*prime(3) = prime(5). It's interesting that we also have 2*4 - 1*3 = 5. [Firoozbakht]

π(1) + π(2) + π(3) + π(4) + π(5) = phi(1 + 2 + 3 + 4 + 5). It is the only number with this property. [Firoozbakht]