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A unique prime indeed. Reverse the order of its middle digits to form the next unique prime (9901). The greatest prime factor of any 10digit repdigit is 9091. [La Haye] The smallest prime of the form 10k10^(k1).....+10^0, for k=4. [Silva] 9091, 909091, 909090909090909091, and 909090909090909090909090909091 are each prime, and 9091 and 909091 are the two smallest prime factors of 9090909090909090909090909090909091. Submitted on 9/09/09. [Green] The lesser in the only pair of primes, (9091, 9293), formed from four successive doubledigit composite numbers, 90, 91, 92, 93. [Loungrides]
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