A056659 - OEIS

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A056659

Numbers n such that 10*R_n + 9 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 4, 5, 7, 16, 49, 683, 719, 1451, 1678, 3145 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (10^(n+1)+71)/9 is prime.`
	LINKS	`Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[10*(10^n - 1)/9 + 9], Print[n]], {n, 5000}]`
	CROSSREFS	`See A097685 for another version.` `Sequence in context: A106170 A085195 A107289 * A049896 A029520 A123368` `Adjacent sequences: A056656 A056657 A056658 * A056660 A056661 A056662`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 09 2000`

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Last modified February 15 17:46 EST 2012. Contains 205835 sequences.