179

This number is a prime.

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The only non-titanic prime (emirp) of the form p = 7^x + x^7 + x, where x is a prime (x=2). [Loungrides]

The sum of all the double-digit primes, each consisting of successive digits in ascending order, is an emirp, i.e., 23 + 67 + 89 = 179. Note that the concatenation of these three primes in descending order, i.e., 896723 is a prime. [Loungrides]