A056720 - OEIS

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A056720

Numbers n such that 7*10^n + 3*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 2, 3, 5, 53, 56, 343, 908, 1079, 2204, 2379, 9134, 9371, 9728 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,3`
	COMMENTS	`Also numbers n such that (22*10^n-1)/3 is prime.`
	LINKS	`Makoto Kamada, Factorizations of 733...33` `Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 710^n + 3(10^n-1)/9], Print[n]], {n, 0, 5000}]`
	CROSSREFS	`Sequence in context: A060380 A062608 A041791 * A100850 A060085 A114370` `Adjacent sequences: A056717 A056718 A056719 * A056721 A056722 A056723`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 11 2000`
	EXTENSIONS	`More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008`

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Last modified February 16 11:51 EST 2012. Contains 205908 sequences.