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A056719
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Numbers n such that 7*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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OFFSET
| 1,3
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COMMENTS
| Also numbers n such that (64*10^n-1)/9 is prime.
No other terms below 184000 [From Serge Batalov (batalovs(AT)yahoo.com), Aug 13 2009]
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LINKS
| Makoto Kamada, Factorizations of 711...11
Index entries for primes involving repunits
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MATHEMATICA
| Do[ If[ PrimeQ[ 7*10^n + (10^n-1)/9], Print[n]], {n, 0, 35076}]
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CROSSREFS
| Sequence in context: A197228 A009521 A116120 * A038855 A097254 A043911
Adjacent sequences: A056716 A056717 A056718 * A056720 A056721 A056722
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KEYWORD
| hard,nonn
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 11 2000
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EXTENSIONS
| A new PRP term from Serge Batalov (batalovs(AT)yahoo.com), Aug 13 2009
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