A099420 - OEIS

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A099420

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

1, 2, 3, 5, 9, 12, 15, 21, 264, 383, 2720, 4494 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (7*10^n-43)/9 is prime.`
	LINKS	`Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 7(10^n - 1)/9 - 4], Print[n]], {n, 0, 5000}]`
	CROSSREFS	`Sequence in context: A141403 A124204 A161412 * A184794 A144728 A051147` `Adjacent sequences: A099417 A099418 A099419 * A099421 A099422 A099423`
	KEYWORD	`nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 14 2004`

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Last modified February 15 21:07 EST 2012. Contains 205856 sequences.