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A103008
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Numbers n such that 5*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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1
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2, 9, 12, 15, 26, 45, 62, 80, 128, 326, 494, 614, 710, 1641, 1646, 2103, 8514, 8688
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OFFSET
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1,1
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COMMENTS
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Also numbers n such that (47*10^n-11)/9 is prime.
No other terms below 50000.
a(19) > 10^5. - Robert Price, Jul 04 2015
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LINKS
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Table of n, a(n) for n=1..18.
Makoto Kamada, Prime numbers of the form 522...221.
Index entries for primes involving repunits.
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FORMULA
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a(n) = A101573(n) + 1.
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MATHEMATICA
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Do[ If[ PrimeQ[(47*10^n - 11)/9], Print[n]], {n, 0, 10000}]
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CROSSREFS
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Cf. A002275, A101573.
Sequence in context: A207967 A265413 A297830 * A124742 A152003 A251428
Adjacent sequences: A103005 A103006 A103007 * A103009 A103010 A103011
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KEYWORD
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more,nonn
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AUTHOR
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Robert G. Wilson v, Jan 18 2005
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STATUS
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approved
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