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A056716
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Numbers n such that 6*10^n-1 is prime.
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4
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0, 1, 2, 4, 5, 7, 10, 13, 22, 23, 28, 34, 40, 61, 73, 361, 490, 613, 1624, 2000, 2994, 4301, 4332, 18668, 32544, 34936
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Also numbers n such that 5*10^n + 9*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Next term is > 15000. - Hugo Pfoertner (hugo(AT)pfoertner.org), Feb 12 2004
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LINKS
| Makoto Kamada, Factorizations of 599...99
Index entries for primes involving repunits
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MATHEMATICA
| Do[ If[ PrimeQ[ 6*10^n - 1], Print[n]], {n, 0, 5000}]
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CROSSREFS
| Cf. A056805 (6*10^n+1 is prime).
Sequence in context: A036559 A083022 A062463 * A190235 A023181 A123065
Adjacent sequences: A056713 A056714 A056715 * A056717 A056718 A056719
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KEYWORD
| hard,nonn,more
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 11 2000
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EXTENSIONS
| More terms from Hugo Pfoertner (hugo(AT)pfoertner.org), Feb 12 2004
3 more terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 30 2007
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