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GIMPS has discovered a new largest known prime number: 2^{82589933}1 (24,862,048 digits) 169 = (2^{7} + 7^{2})  (7 + 1) and is the smallest perfect square of the form (2^{p} + p^{2})  (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] The sum of first five emirps can be represented as the square of the first emirp. [Loungrides] The lucky numbers of Euler are well known. But what will happen if we change the formula a little? Consider A = 169  n  n^2. The expression A is prime for n = 1 to 12 and A is prime for n = 1 to 24. Do you know another number which give the same results except 4, 9, 25 and 49? [Petrov] The smallest square such that every digit (d) repeated d times gives prime. Note that the same is true if we reverse or invert the digits of the number 169, i.e. 1666666999999999, 9999999996666661 and 6666669999999991 are all primes. [Petrov]
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