A099419 - OEIS

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A099419

Numbers n such that 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

2, 13, 20, 23, 31, 100, 241, 275, 925, 1067, 1369, 2065, 7163 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,1`
	COMMENTS	`Also numbers n such that (7*10^n-61)/9 is prime.`
	LINKS	`Index entries for primes involving repunits` `Makoto Kamada, Factorizations of 77...771.`
	FORMULA	`a(n)=A056688(n)+1 - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008`
	MATHEMATICA	`Do[ If[ PrimeQ[ 7(10^n - 1)/9 - 6], Print[n]], {n, 0, 7000}]`
	CROSSREFS	`Sequence in context: A121181 A007355 A105452 * A061871 A084651 A085509` `Adjacent sequences: A099416 A099417 A099418 * A099420 A099421 A099422`
	KEYWORD	`nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 14 2004`
	EXTENSIONS	`7163 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008`

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Last modified February 17 19:13 EST 2012. Contains 206085 sequences.