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A059677
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Numbers n such that 1n1, 3n3, 7n7 and 9n9 are all primes.
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2
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20, 53, 341, 536, 2312, 2477, 3380, 3665, 3686, 4547, 5009, 5105, 6458, 6488, 6731, 6845, 7499, 7508, 7562, 7835, 8411, 8831, 9032, 9386, 9764, 9839, 11027, 11885, 14990, 19589, 20498, 21080, 22844, 24821, 25220, 26393, 27593, 29864, 29921
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OFFSET
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1,1
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LINKS
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EXAMPLE
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2312 is a term because 123121, 323123, 723127 and 923129 are all primes.
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MATHEMATICA
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Select[ Range[ 30000 ], PrimeQ[ ToExpression[ StringInsert[ ToString[ # ], "1", {1, -1} ] ] ] && PrimeQ[ ToExpression[ StringInsert[ ToString[ # ], "3", {1, -1} ] ] ] && PrimeQ[ ToExpression[ StringInsert[ ToString[ # ], "7", {1, -1} ] ] ] && PrimeQ[ ToExpression[ StringInsert[ ToString[ # ], "9", {1, -1} ] ] ] & ]
enclose[n_]:=Table[FromDigits[Join[{i}, IntegerDigits[n], {i}]], {i, {1, 3, 7, 9}}]; Select[Range[30000], AllTrue[enclose[#], PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Mar 21 2015 *)
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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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EXTENSIONS
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STATUS
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approved
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