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A096506
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Numbers n for which 2*R_n + 1 is a prime, where R_n = 11...1 is the repunit (A002275) of length n.
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6
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1, 2, 3, 8, 11, 36, 95, 101, 128, 260, 351, 467, 645, 1011, 1178, 1217, 2442, 3761, 3806
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also numbers n such that (2*10^n+7)/9 is prime.
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LINKS
| Index entries for primes involving repunits
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EXAMPLE
| n=36: 222222222222222222222222222222222223 is a prime number.
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MATHEMATICA
| Do[ If[ PrimeQ[ 2(10^n - 1)/9 + 1], Print[n]], {n, 7000}] (from Robert G. Wilson v Oct 14 2004)
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CROSSREFS
| Cf. A096503, A096504, A096505, A096506, A096507, A096508.
Sequence in context: A143914 A041123 A042045 * A119155 A119195 A119199
Adjacent sequences: A096503 A096504 A096505 * A096507 A096508 A096509
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KEYWORD
| base,nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Jul 12 2004
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