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A056721
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Numbers n such that 8*10^n-1 is prime.
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2
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0, 1, 4, 5, 8, 10, 25, 49, 76, 128, 175, 238, 550, 796, 1219, 2012, 2846, 11336, 21296, 49808, 74318
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Also numbers n such that 7*10^n + 9*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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LINKS
| Makoto Kamada, Factorizations of 799...99
Index entries for primes involving repunits
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MATHEMATICA
| Do[ If[ PrimeQ[ 7*10^n + (10^n-1)], Print[n]], {n, 0, 3000}]
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CROSSREFS
| Sequence in context: A022435 A190394 A116050 * A057479 A050140 A190860
Adjacent sequences: A056718 A056719 A056720 * A056722 A056723 A056724
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KEYWORD
| hard,nonn,more
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 11 2000
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EXTENSIONS
| More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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