A056664 - OEIS

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A056664

Numbers n such that 80*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

2, 18, 78, 138, 222, 462, 543, 1095, 1418, 3246, 3876, 4416, 9506, 11090, 14601 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,1`
	COMMENTS	`Also numbers n such that (8*10^(n+1)-71)/9 is prime.`
	LINKS	`Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 80*(10^n - 1)/9 + 1 ], Print[n]], {n, 15000}]`
	CROSSREFS	`Cf. A092675 (corresponding primes).` `Sequence in context: A197093 A034473 A024171 * A064057 A176496 A091940` `Adjacent sequences: A056661 A056662 A056663 * A056665 A056666 A056667`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 09 2000`
	EXTENSIONS	`1415 (giving a probable prime) from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Mar 02 2004. There are no other terms <= 2500.`

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Last modified February 15 07:42 EST 2012. Contains 205717 sequences.