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A056663
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Numbers n such that 80*R_n + 9 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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1
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1, 13, 16, 34, 4174, 4471, 9811, 12259, 12340, 13759, 14575
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also numbers n such that (8*10^(n+1)+1)/9 is prime.
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LINKS
| Index entries for primes involving repunits
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MATHEMATICA
| Do[ If[ PrimeQ[ 80*(10^n - 1)/9 + 9 ], Print[n]], {n, 0, 30000}]
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CROSSREFS
| Sequence in context: A163674 A132947 A205876 * A103230 A107081 A029526
Adjacent sequences: A056660 A056661 A056662 * A056664 A056665 A056666
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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
| Intermediate missing terms 9811 (from M.Kamada), 12259, 12340, 13759 added by Serge Batalov (batalovs(AT)yahoo.com), Dec 14 2008
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