A099412 - OEIS

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A099412

Numbers n such that 4*R_n - 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 2, 4, 11, 28, 55, 94, 475, 2080, 4835, 5845 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (4*10^n-31)/9 is prime.`
	LINKS	`Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 4(10^n - 1)/9 - 3], Print[n]], {n, 0, 7000}]`
	CROSSREFS	`Sequence in context: A131482 A148131 A205504 * A100094 A099525 A024742` `Adjacent sequences: A099409 A099410 A099411 * A099413 A099414 A099415`
	KEYWORD	`nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 14 2004`

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Last modified February 14 18:47 EST 2012. Contains 205663 sequences.