A102984 - OEIS

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A102984

Numbers n such that 4*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 4, 7, 22, 23, 80, 4427 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (38*10^n-11)/9 is prime.`
	LINKS	`Table of n, a(n) for n=1..8.` `Makoto Kamada, Factorizations of 422...221.` `Index entries for primes involving repunits.`
	MATHEMATICA	`Do[ If[ PrimeQ[(38*10^n - 11)/9], Print[n]], {n, 0, 10000}]`
	CROSSREFS	`Sequence in context: A145777 A188497 A153550 * A103017 A091833 A171978` `Adjacent sequences: A102981 A102982 A102983 * A102985 A102986 A102987`
	KEYWORD	`more,nonn`
	AUTHOR	`Robert G. Wilson v, Dec 22 2004`
	STATUS	`approved`

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Last modified May 20 09:16 EDT 2013. Contains 225458 sequences.