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A056726
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Numbers n such that 9*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
| 1,1
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COMMENTS
| Also numbers n such that (82*10^n-1)/9 is prime.
The next term is > 10000. - 8570 from Hugo Pfoertner (hugo(AT)pfoertner.org), Oct 22 2004
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LINKS
| Makoto Kamada, Factorizations of 911...11
Index entries for primes involving repunits
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MATHEMATICA
| Do[ If[ PrimeQ[ 9*10^n + (10^n-1)/9], Print[n]], {n, 0, 5000}]
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CROSSREFS
| Sequence in context: A136898 A077138 A192164 * A176042 A185593 A136899
Adjacent sequences: A056723 A056724 A056725 * A056727 A056728 A056729
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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
| 8570 from Hugo Pfoertner (hugo(AT)pfoertner.org), Oct 22 2004
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