The book is now available! 654781329
(another Prime Pages' Curiosity)
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+ 654781329 = 3^2 x 72753481 is the only integer with just two distinct prime factors, which is also "penholodigital" (using each nonzero digit once and only once) and whose reversal is a square: 923187456 = 2^8 x 3^4 x 211^2 = 30384^2. [Post]




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