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A056662
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Numbers n such that 90*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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2
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0, 1, 2, 16, 139, 989, 1886, 3529, 5995, 13819, 21872, 26044
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OFFSET
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1,3
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COMMENTS
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Also numbers n such that 10^(n+1) - 3 is a prime number.
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LINKS
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Table of n, a(n) for n=1..12.
Index entries for primes involving repunits
Makoto Kamada, Factorizations of 99...997.
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MATHEMATICA
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Do[ If[ PrimeQ[ 90*(10^n - 1)/9 + 7 ], Print[n]], {n, 0, 1250}]
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CROSSREFS
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Sequence in context: A001252 A067058 A002302 * A151402 A199565 A003768
Adjacent sequences: A056659 A056660 A056661 * A056663 A056664 A056665
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KEYWORD
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hard,nonn
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AUTHOR
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Robert G. Wilson v, Aug 09 2000
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EXTENSIONS
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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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STATUS
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approved
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