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Search: id:A056712
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| A056712 |
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Numbers n such that 5*10^n-1 is prime. |
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+0
3
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| 2, 3, 4, 6, 14, 54, 210, 390, 594, 3460, 5028, 5219, 5332, 8072, 15796, 16131, 21456, 29282, 78790, 85142
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Also numbers n such that 4*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 499...99
Index entries for primes involving repunits
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MATHEMATICA
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Do[ If[ PrimeQ[ 4*10^n + (10^n-1)], Print[n]], {n, 0, 4660}]
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CROSSREFS
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Sequence in context: A038767 A095991 A049911 this_sequence A002087 A049288 A102946
Adjacent sequences: A056709 A056710 A056711 this_sequence A056713 A056714 A056715
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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: 8072, 15796, 16131, 29282.
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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