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A number that can be expressed as the signed sum of cubes in at least three ways: 264488^{3} + 331574^{3}  380193^{3} =
2322404^{3}  869418^{3}  2281057^{3} = 402906^{3}  211402^{3}  382489^{3}. [Rupinski]
The smallest prime such that another prime is never produced by inserting the same digit between each pair of its digits (40309, 41319, 42329, ... , 49399, are all composite). [Noll] Take the sum of emirp 439 and its reversal: 439 + 934 = 1373. If we split 1373 in half and factor, we get 13*73 = 949 = 227+722 (a prime and its reversal). Note that 439+722 = 1161 = 934+227 uses each of the above primes and their reversals. [Bergot]
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