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A056684
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Numbers n such that 50*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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3
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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 (5*10^(n+1)-41)/9 is prime.
a(4) > 10^5. - Robert Price, Nov 16 2014
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LINKS
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Table of n, a(n) for n=1..3.
Makoto Kamada, Prime numbers of the form 55...551.
Index entries for primes involving repunits
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FORMULA
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a(n) = A099415(n) - 1. - Robert Price, Nov 16 2014
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MATHEMATICA
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Do[ If[ PrimeQ[50*(10^n - 1)/9 + 1], Print[n]], {n, 15000}]
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CROSSREFS
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Cf. A002275, A099415.
Sequence in context: A262515 A041607 A042097 * A042731 A087304 A340204
Adjacent sequences: A056681 A056682 A056683 * A056685 A056686 A056687
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KEYWORD
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hard,nonn,bref,more
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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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