A056724 - OEIS

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A056724

Numbers n such that 8*10^n + 7*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.

2, 9, 15, 32, 38, 65, 123, 173, 257, 320, 326, 639, 719, 774, 902 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,1`
	COMMENTS	`Also numbers n such that (79*10^n-7)/9 is prime.`
	LINKS	`Makoto Kamada, Factorizations of 877...77` `Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 810^n + 7(10^n-1)/9], Print[n]], {n, 0, 10000}]`
	CROSSREFS	`Sequence in context: A063105 A063094 A108463 * A083174 A067547 A166374` `Adjacent sequences: A056721 A056722 A056723 * A056725 A056726 A056727`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 11 2000`

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Last modified February 15 15:20 EST 2012. Contains 205823 sequences.