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A097683
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Numbers n such that R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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5
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0, 1, 2, 3, 5, 9, 11, 24, 84, 221, 1314, 2952, 20016
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Also numbers n such that (10^n+17)/9 is prime.
Values indicate primes of the form "(n-1) ones followed by a three"; zero is a degenerate case. Related to the base 10 repunit primes.
No others less than 30000.
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LINKS
| Makoto Kamada, Factorizations of 11...113.
Index entries for primes involving repunits
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EXAMPLE
| 11113 = ((10^5)+17)/9 and 11113 is prime.
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MATHEMATICA
| Do[ If[ PrimeQ[(10^n - 1)/9 + 2], Print[n]], {n, 0, 5951}] (from Robert G. Wilson v Oct 15 2004)
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CROSSREFS
| Cf. A004023, A097684, A097685.
Sequence in context: A101737 A176550 A019276 * A141403 A124204 A161412
Adjacent sequences: A097680 A097681 A097682 * A097684 A097685 A097686
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KEYWORD
| more,nonn
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AUTHOR
| Carl R. White (cyrek(AT)cyreksoft.yorks.com) and Julien Peter Benney (jpbenney(AT)ftml.net), Aug 19 2004
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EXTENSIONS
| a(10) from Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 15 2004
Edited by N. J. A. Sloane, Apr 02 2009, at the suggestion of Farideh Firoozbakht
a(11) from Kamada link by Ray Chandler (rayjchandler(AT)sbcglobal.net), Dec 23 2010
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