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A056723
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Numbers n such that 8*10^n + 3*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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1, 7, 23, 29, 133, 173, 367, 1925, 3707, 5765, 9709, 19573, 43753
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also numbers n such that (25*10^n-1)/3 is prime.
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LINKS
| Makoto Kamada, Factorizations of 833...33
Index entries for primes involving repunits
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MATHEMATICA
| Do[ If[ PrimeQ[ 8*10^n + 3*(10^n-1)/9], Print[n]], {n, 0, 10000}]
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CROSSREFS
| Cf. A093676.
Sequence in context: A095314 A038948 A019389 * A080802 A078515 A044449
Adjacent sequences: A056720 A056721 A056722 * A056724 A056725 A056726
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KEYWORD
| nonn,changed
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 11 2000
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EXTENSIONS
| Corrected by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
19573 and 43753 from Serge Batalov, Jan 2009 confirmed as next terms by Ray Chandler (rayjchandler(AT)sbcglobal.net), Feb 13 2012
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