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A056657
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Numbers n such that 60*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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8
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0, 1, 5, 7, 8, 10, 19, 22, 40, 62, 65, 118, 121, 148, 251, 283, 304, 591, 745, 874, 1203, 1363, 2239, 2402, 5105, 5775, 5812, 12455, 14234
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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LINKS
| Index entries for primes involving repunits
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EXAMPLE
| 7, 67, 666667, 66666667, 666666667, 66666666667, etc. are primes.
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MATHEMATICA
| Do[ If[ PrimeQ[ 60*(10^n - 1)/9 + 7 ], Print[n]], {n, 25556}]
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CROSSREFS
| Equals A096507 - 1.
Sequence in context: A080707 A059612 A192270 * A068312 A082097 A088299
Adjacent sequences: A056654 A056655 A056656 * A056658 A056659 A056660
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KEYWORD
| hard,nonn
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 09 2000
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 22 2003
2239,2402,5105,5775 from Farideh Firoozbakht (f.firoozbakht(AT)sci.ui.ac.ir), Dec 23 2003
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