A056681 - OEIS

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A056681

Numbers n such that 40*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 3, 10, 27, 54, 93, 474, 2079, 4834, 5844 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (4*10^(n+1)-31)/9 is prime.`
	LINKS	`Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[40*(10^n - 1)/9 + 1], Print[n]], {n, 0, 7000}]`
	CROSSREFS	`Sequence in context: A110158 A196232 A105660 * A192959 A100624 A088809` `Adjacent sequences: A056678 A056679 A056680 * A056682 A056683 A056684`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 10 2000`

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Last modified February 17 06:11 EST 2012. Contains 205989 sequences.