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Search: id:A056721
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| A056721 |
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Numbers n such that 8*10^n-1 is prime. |
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+0
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; listen)
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OFFSET
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1,3
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COMMENT
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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
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Makoto Kamada, Factorizations of 799...99
Index entries for primes involving repunits
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MATHEMATICA
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Do[ If[ PrimeQ[ 7*10^n + (10^n-1)], Print[n]], {n, 0, 3000}]
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CROSSREFS
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Sequence in context: A139132 A022435 A116050 this_sequence A057479 A050140 A047376
Adjacent sequences: A056718 A056719 A056720 this_sequence A056722 A056723 A056724
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KEYWORD
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hard,nonn
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AUTHOR
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Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 11 2000
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EXTENSIONS
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Other known primes: 11336, 49808.
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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