All multi-digit primes must end in 1, 3, 7 or 9. For a three-digit number in all its three-digital permutations to remain prime, the three digits must be composed of 2 or 3 of these given digits. There are three sets of such primes: (113, 131, 311), (199, 919, 991), and (337, 373, 733).
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