8311

This number is a prime.

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The largest prime formed from a double-digit prime followed by the sum of its digits. Note that this sum is another prime. [Loungrides]

8311, 83, 11 and the sums of their digits, i.e., 13, 11, 2 are primes. Note that the reversal of the power 83^11 = 1287831418538085836267,, i.e., 7626385808358141387821 is also prime and 8311 is the smallest prime with this property. [Loungrides]