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A099005
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Numbers k such that 4*10^k + 6*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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2
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1, 2, 3, 4, 6, 7, 8, 12, 23, 59, 75, 144, 204, 268, 760, 1216, 1430, 1506, 1509, 2804, 2924, 3201, 3305, 5753, 9268, 11279, 19677, 23414, 28627, 31362, 42299, 49119, 63747, 81767, 111443, 263720, 264791
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OFFSET
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1,2
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COMMENTS
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Also numbers k such that (14*10^k - 11)/3 is a prime number.
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LINKS
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FORMULA
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EXAMPLE
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For n = 1, 2, 3, 4, 6, 7, 8 are members since 43, 463, 4663, 46663, 4666663, 46666663 and 466666663 are primes.
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MATHEMATICA
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Do[ If[ PrimeQ[(14*10^n - 11)/3], Print[n]], {n, 0, 10000}] (* Robert G. Wilson v, Dec 17 2004 *)
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CROSSREFS
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KEYWORD
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more,nonn
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AUTHOR
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Julien Peter Benney (jpbenney(AT)ftml.net), Nov 07 2004
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EXTENSIONS
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a(26)-a(27) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(30)-a(32) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013
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STATUS
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approved
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