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A056706
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Numbers k such that 4*10^k + 1*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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1
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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 (37*10^k - 1)/9 is prime.
a(11) > 10^5. - Robert Price, Nov 30 2014
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LINKS
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Table of n, a(n) for n=1..10.
Makoto Kamada, Prime numbers of the form 411...11.
Index entries for primes involving repunits
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MATHEMATICA
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Do[ If[ PrimeQ[ 4*10^n + (10^n-1)/9], Print[n]], {n, 0, 10000}]
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CROSSREFS
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Cf. A002275, A068815.
Sequence in context: A146379 A056714 A120074 * A052454 A330718 A284108
Adjacent sequences: A056703 A056704 A056705 * A056707 A056708 A056709
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KEYWORD
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hard,nonn
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AUTHOR
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Robert G. Wilson v, Aug 10 2000
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STATUS
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approved
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