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A098960
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Numbers k such that 2*10^k + 7*R_k - 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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1
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2, 6, 33, 69, 150, 936, 3135, 5838, 6990, 20786, 57138
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OFFSET
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1,1
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COMMENTS
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Also numbers k such that (25*10^k - 61)/9 is prime.
a(12) > 10^5. - Robert Price, Feb 27 2015
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LINKS
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Table of n, a(n) for n=1..11.
Makoto Kamada, Prime numbers of the form 277...771.
Index entries for primes involving repunits.
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FORMULA
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a(n) = A101966(n) + 1.
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EXAMPLE
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For n = 2 and 6, we get 271 and 2777771 which are primes.
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MATHEMATICA
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Do[ If[ PrimeQ[(25*10^n - 61)/9], Print[n]], {n, 0, 10000}]
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CROSSREFS
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Cf. A002275, A101966.
Sequence in context: A213435 A083666 A083126 * A162429 A279461 A243324
Adjacent sequences: A098957 A098958 A098959 * A098961 A098962 A098963
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KEYWORD
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more,nonn
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AUTHOR
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Julien Peter Benney (jpbenney(AT)ftml.net), Oct 22 2004
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EXTENSIONS
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a(6) from Ray Chandler, Nov 04 2004
a(7), a(8) & a(9) from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 03 2004
Addition of a(10) from Kamada data by Robert Price, Dec 13 2010
a(11) from Robert Price, Feb 27 2015
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STATUS
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approved
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