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A056713
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Numbers n such that 5*10^n + R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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1
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0, 5, 12, 15, 84, 144, 150, 1235, 1727, 1812, 8687
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OFFSET
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1,2
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COMMENTS
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Also numbers n such that (46*10^n-1)/9 is prime.
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LINKS
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Table of n, a(n) for n=1..11.
Makoto Kamada, Factorizations of 511...11
Index entries for primes involving repunits
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MATHEMATICA
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Do[ If[ PrimeQ[ 5*10^n + (10^n-1)/9], Print[n]], {n, 0, 10000}]
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CROSSREFS
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Sequence in context: A087090 A161756 A184399 * A110670 A111523 A078231
Adjacent sequences: A056710 A056711 A056712 * A056714 A056715 A056716
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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 11 2000
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EXTENSIONS
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8687 from Hugo Pfoertner, Oct 19 2004
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STATUS
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approved
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