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The smallest prime for which the sum of the squares of its digits is also a prime throughout 5 iterations (6 "generations"): 28999999999 > 797 > 179 > 131 > 11 > 2. Terry Trotter called this type of prime a "father" prime, and the subsequent sums (797, 179, 131, 11, 2) "child" primes. Is there a 7generation father prime to be found? [Ganson]
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