3257

This number is a prime.

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The only known emirp formed by concatenating two Fermat primes (3 and 257). [Loungrides]

The smallest prime-digit emirp, containing all the prime digits, that remains an emirp when sandwiched between two identical prime digits, i.e., 332573. [Loungrides]

The only prime-digit prime (emirp) formed from a 2-digit number, (32), following the procedure “each next digit can be represented as the sum of its two previous digits.” [Loungrides]