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A111247
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Numbers n such that (31*10^n - 121) / 9 is prime.
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0
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2, 6, 8, 21, 66, 84, 86, 89, 93, 104, 170, 249, 273, 413, 824, 1392, 1589, 1679, 3125, 3185, 3482, 4089, 4772
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Variant of repunit primes: each value is 3444...44431, with n-2 4's.
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EXAMPLE
| 6 is there because 3444431 is prime.
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MATHEMATICA
| Select[Range[1200], PrimeQ[(31*10^#-121)/9]&] (* From Vladimir Joseph Stephan Orlovsky, Feb 01 2012 *)
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CROSSREFS
| Sequence in context: A185165 A058775 A103023 * A045656 A129342 A045654
Adjacent sequences: A111244 A111245 A111246 * A111248 A111249 A111250
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KEYWORD
| nonn,changed
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AUTHOR
| Joao da Silva (zxawyh66(AT)yahoo.com), Oct 31 2005
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EXTENSIONS
| Edited by Don Reble (djr(AT)nk.ca), Nov 09 2005
a(16) - a(23) from Vladimir Joseph Stephan Orlovsky, Feb 01 2012.
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