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A174441
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Primes p such that the concatenations p//1331 and 1331//p are both prime numbers (for naturals see A174355).
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3
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53, 347, 431, 641, 647, 821, 1709, 1973, 2081, 2591, 2657, 2963, 4073, 4139, 4643, 4787, 5039, 5483, 5657, 6029, 6791, 6917, 6959, 7127, 7673, 8273, 8693, 8807, 8849, 9221, 9311, 9689, 10139, 10457, 11423, 12503, 12743, 13619, 13913, 14549
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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531331 = prime(43928), 133153 = prime(12427) => p(1) = 53 = prime(16).
3471331 = prime(248286), 1331347 = prime(102237) => p(2) = 347 = prime(69).
139131331 = prime(7865788), 133113913 = prime(7544750) => p(39) = 13913 = prime(1645).
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MATHEMATICA
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Select[Prime[Range[2000]], AllTrue[{#*10^4+1331, 1331*10^IntegerLength[ #]+#}, PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, May 08 2016 *)
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PROG
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(PARI) isok(n) = isprime(n) && isprime(n*10^4 + 1331) && isprime(1331*10^(length(Str(n))) + n); \\ Michel Marcus, Aug 27 2013
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Mar 20 2010
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STATUS
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approved
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