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A102502
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Values of n for which the concatenation 9nn9 (from sequence A102484) are primes.
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3
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10, 13, 16, 17, 20, 23, 28, 31, 35, 37, 46, 53, 56, 61, 65, 68, 74, 82, 94, 95, 98, 1010, 1013, 1018, 1042, 1048, 1051, 1052, 1063, 1072, 1073, 1082, 1103, 1114, 1124, 1129, 1139, 1142, 1171, 1192, 1193, 1195, 1208, 1214, 1240, 1241, 1244, 1249, 1258, 1271
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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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The number 910109 is prime and corresponds to n=10.
The number 9101310139 is prime and corresponds to n=1013.
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MATHEMATICA
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fQ[n_] := Block[{id = IntegerDigits[n]}, PrimeQ[ FromDigits[ Join[{9}, id, id, {9}]]]]; Select[ Range[1288], fQ[ # ] &] (* Robert G. Wilson v, Jan 14 2004 *)
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CROSSREFS
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The full sequence of integers of the form 9nn9 is A102484. The primes that correspond to these values of n are sequence A102503.
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KEYWORD
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easy,nonn,base
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AUTHOR
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Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005
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EXTENSIONS
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STATUS
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approved
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