A056656 - OEIS

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A056656

Numbers n such that 20*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 2, 7, 10, 35, 94, 100, 127, 259, 350, 466, 644, 1010, 1177, 1216, 2441, 3760, 3805, 15616, 26458 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,3`
	COMMENTS	`Also numbers n such that (2*10^(n+1)+7)/9 is prime.`
	LINKS	`Makoto Kamada, Prime numbers of the form 22...223` `Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 20*(10^n - 1)/9 + 3 ], Print[n]], {n, 7000}]`
	CROSSREFS	`Cf. A093162 (corresponding primes).` `Sequence in context: A091295 A084184 A015963 * A151346 A110739 A179117` `Adjacent sequences: A056653 A056654 A056655 * A056657 A056658 A056659`
	KEYWORD	`nonn,changed`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 09 2000`
	EXTENSIONS	`2441 from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Mar 27 2004` `15616 and 26458 from Erik Branger, Jan 31 2010`

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Last modified February 16 07:36 EST 2012. Contains 205877 sequences.