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A098930
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Numbers n such that 2*10^n + 5*R_n - 4 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 (23*10^n-41)/9 is prime.
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LINKS
| Makoto Kamada, Factorizations of 255...551.
Index entries for primes involving repunits.
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EXAMPLE
| If n = 3 we get 2551, which is prime.
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MATHEMATICA
| Do[ If[ PrimeQ[(23*10^n - 41)/9], Print[n]], {n, 0, 10000}]
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CROSSREFS
| Sequence in context: A125877 A118787 A191783 * A075372 A064725 A100330
Adjacent sequences: A098927 A098928 A098929 * A098931 A098932 A098933
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KEYWORD
| more,nonn
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AUTHOR
| Julien Peter Benney (jpbenney(AT)ftml.net), Oct 20 2004
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EXTENSIONS
| a(7) from Ray Chandler (rayjchandler(AT)sbcglobal.net), Nov 04 2004
a(8) & a(9) from Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 17 2004
Addition of a(10) from Kamada data by Robert Price (pamandbobprice(AT)yahoo.com), Dec 13 2010
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