A056695 - OEIS

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A056695

Numbers n such that 80*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 2, 3, 5, 8, 11, 71, 117, 123, 189, 243, 303, 356, 1421, 2690, 5537, 7580 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (8*10^(n+1)-17)/9 is prime.`
	LINKS	`Index entries for primes involving repunits` `Makoto Kamada, Factorizations of 88...887.`
	MATHEMATICA	`Do[ If[ PrimeQ[80*(10^n - 1)/9 + 7], Print[n]], {n, 0, 5000}]`
	CROSSREFS	`Sequence in context: A114831 A092362 A105766 * A020899 A057987 A176746` `Adjacent sequences: A056692 A056693 A056694 * A056696 A056697 A056698`
	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 15 03:59 EST 2012. Contains 205694 sequences.