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A099419
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Numbers n such that 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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2
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2, 13, 20, 23, 31, 100, 241, 275, 925, 1067, 1369, 2065, 7163, 37963, 91856, 111706, 260198, 271757
(list;
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refs;
listen;
history;
text;
internal format)
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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 (7*10^n-61)/9 is prime.
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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 77...771.
Index entries for primes involving repunits
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FORMULA
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a(n) = A056688(n) + 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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MATHEMATICA
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Do[ If[ PrimeQ[ 7(10^n - 1)/9 - 6], Print[n]], {n, 0, 7000}]
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CROSSREFS
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Cf. A093176.
Sequence in context: A007355 A105452 A219278 * A061871 A182459 A084651
Adjacent sequences: A099416 A099417 A099418 * A099420 A099421 A099422
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KEYWORD
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nonn
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AUTHOR
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Robert G. Wilson v, Oct 14 2004
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EXTENSIONS
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a(13) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(14)-a(15) from Erik Branger, Dec 19 2009
a(16) from Erik Branger, Jan 29 2011
a(17) from Erik Branger, Nov 26 2011
a(18) from Erik Branger, Mar 05 2012
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STATUS
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approved
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