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A097684
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Numbers k such that (10^k - 1)/9 + 6 is prime.
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3
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1, 2, 4, 5, 8, 23, 29, 40, 131, 136, 215, 611, 767, 2153, 2576, 22973, 42689, 85712, 85864, 112067, 538508, 631715
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OFFSET
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1,2
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COMMENTS
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Values indicate primes of the form "(k-1) ones followed by a seven". Related to the base-10 repunit primes.
Some of the larger entries may only correspond to probable primes.
Corresponding primes are equal to (10^k + 53)/9. - Robert Price, Jan 11 2015
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LINKS
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FORMULA
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a(n) = A056655(n) + 1 for all n >= 0.
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MATHEMATICA
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Do[ If[ PrimeQ[(10^n - 1)/9 + 6], Print[n]], {n, 0, 5000}] (* Robert G. Wilson v, Oct 14 2004 *)
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PROG
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(PARI) for (i=1, 1000, if(isprime((10^i-1)/9 + 6), print1(i, ", "))) \\ Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Aug 23 2004
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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a(12)-a(13) from Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Aug 23 2004
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STATUS
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approved
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