A056708 - OEIS

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A056708

Numbers n such that 4*10^n + 7*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 4, 13, 25, 36, 357, 373, 1041, 1089, 1093, 1297, 8274 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (43*10^n-7)/9 is prime.`
	LINKS	`Makoto Kamada, Factorizations of 477...77` `Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 410^n + 7(10^n-1)/9], Print[n]], {n, 0, 6000}]`
	CROSSREFS	`Sequence in context: A085018 A001741 A154820 * A092484 A091823 A024834` `Adjacent sequences: A056705 A056706 A056707 * A056709 A056710 A056711`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 10 2000`
	EXTENSIONS	`8274 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008`

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Last modified February 15 02:49 EST 2012. Contains 205694 sequences.