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Search: id:A056655
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| A056655 |
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Numbers n such that 10*R_n +7 is prime, where R_n = 11...1 is the repunit (A002275) of length n. |
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+0
3
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| 0, 1, 3, 4, 7, 22, 28, 39, 130, 135, 214, 610, 766, 2152, 2575
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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Also numbers n such that (10^(n+1)+53)/9 is prime.
2575 also produces a probable prime.
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LINKS
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Index entries for primes involving repunits
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FORMULA
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a(n) = A097684(n) - 1 for all n >= 0. - Rick L. Shepherd (rshepherd2(AT)hotmail.com), Aug 23 2004
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MATHEMATICA
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Do[ m = n; If[ primeQ[ 10*(10^n - 1)/9 + 7 ], Print[ n ] ], {n, 1, 1250} ]
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CROSSREFS
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Cf. A093139 (corresponding primes).
Cf. A097684.
Sequence in context: A113534 A030724 A124082 this_sequence A042037 A041091 A117764
Adjacent sequences: A056652 A056653 A056654 this_sequence A056656 A056657 A056658
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KEYWORD
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hard,nonn
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AUTHOR
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Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 09 2000
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EXTENSIONS
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2152 (giving a probable prime) from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Mar 23 2004
2575 from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Aug 23 2004
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