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A102985
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Numbers n such that 4*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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0, 1, 4, 9, 10, 31, 70, 160, 171, 277, 630, 724, 3717, 5542, 5634, 10656, 12724, 31954
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OFFSET
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1,3
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COMMENTS
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Also numbers n such that (38*10^n+7)/9 is prime.
a(19) > 10^5. - Robert Price, May 09 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 422...223.
Index entries for primes involving repunits.
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FORMULA
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a(n) = A101720(n-1) + 1.
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MATHEMATICA
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Do[ If[ PrimeQ[(38*10^n + 7)/9], Print[n]], {n, 0, 10000}]
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CROSSREFS
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Cf. A002275, A101720.
Sequence in context: A141395 A121215 A178224 * A112401 A178360 A197125
Adjacent sequences: A102982 A102983 A102984 * A102986 A102987 A102988
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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 17 2005
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EXTENSIONS
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Addition of a(16)-a(17) from Kamada data by Robert Price, Dec 12 2010
a(18) 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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