A056696 - OEIS

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A056696

Numbers n such that 90*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

2, 4, 6, 32, 44, 104, 196, 198, 280, 300, 316, 1106, 1656, 3394, 35924, 37596, 64304, 80138, 221630 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,1`
	COMMENTS	`Also numbers n such that 10^(n+1) - 9 is a prime.`
	LINKS	`Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[90*(10^n - 1)/9 + 1], Print[n]], {n, 0, 7000}]`
	CROSSREFS	`Sequence in context: A046847 A121069 A100838 * A045662 A195324 A175877` `Adjacent sequences: A056693 A056694 A056695 * A056697 A056698 A056699`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 10 2000`
	EXTENSIONS	`a(15) - a(19) (35924 - 221630) from Alexander Gramolin, May 13 2011`

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