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A098960
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Numbers n such that 2*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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1
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OFFSET
| 1,1
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COMMENTS
| Also numbers n such that (25*10^n-61)/9 is prime.
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LINKS
| Makoto Kamada, Factorizations of 277...771.
Index entries for primes involving repunits.
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EXAMPLE
| For n = 2 and 6, we get 271 and 2777771 which are primes.
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MATHEMATICA
| Do[ If[ PrimeQ[(25*10^n - 61)/9], Print[n]], {n, 0, 10000}]
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CROSSREFS
| Sequence in context: A013976 A083666 A083126 * A162429 A018952 A019028
Adjacent sequences: A098957 A098958 A098959 * A098961 A098962 A098963
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KEYWORD
| more,nonn
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AUTHOR
| Julien Peter Benney (jpbenney(AT)ftml.net), Oct 22 2004
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EXTENSIONS
| a(6) from Ray Chandler (rayjchandler(AT)sbcglobal.net), 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 (pamandbobprice(AT)yahoo.com), Dec 13 2010
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