A056687 - OEIS

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A056687

Numbers n such that 50*R_n + 9 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 7, 11, 17, 25, 31, 137, 187, 221, 337, 1001, 2743, 6529 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (5*10^(n+1)+31)/9 is prime.`
	LINKS	`Index entries for primes involving repunits` `Makoto Kamada, Factorizations of 55...559.`
	MATHEMATICA	`Do[ If[ PrimeQ[50*(10^n - 1)/9 + 9], Print[n]], {n, 0, 5000}]`
	CROSSREFS	`Sequence in context: A088176 A046132 A162337 * A088981 A021014 A021013` `Adjacent sequences: A056684 A056685 A056686 * A056688 A056689 A056690`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 10 2000`
	EXTENSIONS	`More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008`

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Last modified February 17 12:38 EST 2012. Contains 206021 sequences.