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A174355
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Natural numbers n such that the concatenations n//1331 and 1331//n are prime numbers.
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5
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53, 57, 153, 249, 279, 329, 333, 339, 347, 381, 399, 431, 471, 489, 641, 647, 711, 821, 851, 923, 959, 987, 1169, 1239, 1313, 1383, 1479, 1547, 1563, 1589, 1611, 1653, 1677, 1709, 1773, 1863, 1887, 1973, 2031, 2067
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OFFSET
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1,1
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COMMENTS
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REFERENCES
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Marcus du Sautoy: Die Musik der Primzahlen. Auf den Spuren des groessten Raetsels der Mathematik, Beck, Muenchen 2004
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LINKS
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EXAMPLE
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531331 = prime(43928), 133153 = prime(12427), 53 is smallest term of sequence.
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MATHEMATICA
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Select[Range[2100], AllTrue[{#*10^4+1331, 1331*10^IntegerLength[#]+#}, PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Aug 21 2015 *)
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PROG
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(PARI) isok(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 17 2010
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STATUS
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approved
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