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A020471
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Primes that contain digits 7 and 9 only.
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12
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7, 79, 97, 797, 977, 997, 77797, 77977, 77999, 79777, 79979, 79997, 79999, 97777, 777977, 777979, 779797, 797977, 799979, 799999, 999979, 7777997, 7779979, 7779997, 7797799, 7797997, 7799797, 7799999, 7977779, 7977797, 7977799, 7977997
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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Flatten[Table[Select[FromDigits/@Tuples[{7, 9}, n], PrimeQ], {n, 7}]] (* Vincenzo Librandi, Jul 28 2012 *)
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PROG
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(Magma) [p: p in PrimesUpTo(7977997) | Set(Intseq(p)) subset [7, 9]]; // Vincenzo Librandi, Jul 28 2012
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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