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169 (another Prime Pages' Curiosity) |
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169 = (27 + 72) - (7 + 1) and is the smallest perfect square of the form
(2p + p2) - (p + 1). [Charles]
The smallest square that is prime when turned upside down. [Wu] 169 is the first composite Pell number with a prime index. Coincidentally, it is also the last square in the Pell sequence. [Axoy] The sum of first 12 powers of semiprimes is (12+1)^2. [Post]
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