A103008 - OEIS

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A103008

Numbers n such that 5*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

2, 9, 12, 15, 26, 45, 62, 80, 128, 326, 494, 614, 710, 1641, 1646, 2103, 8514, 8688 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,1`
	COMMENTS	`Also numbers n such that (47*10^n-11)/9 is prime.` `No other terms below 50000.` `a(19) > 10^5. - Robert Price, Jul 04 2015`
	LINKS	`Table of n, a(n) for n=1..18.` `Makoto Kamada, Prime numbers of the form 522...221.` `Index entries for primes involving repunits.`
	FORMULA	`a(n) = A101573(n) + 1.`
	MATHEMATICA	`Do[ If[ PrimeQ[(47*10^n - 11)/9], Print[n]], {n, 0, 10000}]`
	CROSSREFS	`Cf. A002275, A101573.` `Sequence in context: A207967 A265413 A297830 * A124742 A152003 A251428` `Adjacent sequences: A103005 A103006 A103007 * A103009 A103010 A103011`
	KEYWORD	`more,nonn`
	AUTHOR	`Robert G. Wilson v, Jan 18 2005`
	STATUS	`approved`

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Last modified February 2 03:29 EST 2024. Contains 369553 sequences. (Running on oeis4.)